cmd/compiler,internal/runtime/atomic: optimize Store{64,32,8} on loong64

cmd/compiler,internal/runtime/atomic: optimize Store{64,32,8} on loong64

On Loong64, AMSWAPDB{W,V} instructions are supported by default, and AMSWAPDB{B,H} [1]
is a new instruction added by LA664(Loongson 3A6000) and later microarchitectures.
Therefore, AMSWAPDB{W,V} (full barrier) is used to implement AtomicStore{32,64}, and
the traditional MOVB or the new AMSWAPDBB is used to implement AtomicStore8 according
to the CPU feature.

The StoreRelease barrier on Loong64 is "dbar 0x12", but it is still necessary to
ensure consistency in the order of Store/Load [2].

LoweredAtomicStorezero{32,64} was removed because on loong64 the constant "0" uses
the R0 register, and there is no performance difference between the implementations
of LoweredAtomicStorezero{32,64} and LoweredAtomicStore{32,64}.

goos: linux
goarch: loong64
pkg: internal/runtime/atomic
cpu: Loongson-3A5000-HV @ 2500.00MHz
                |  bench.old  |              bench.new              |
                |   sec/op    |   sec/op     vs base                |
AtomicStore64     19.61n ± 0%   13.61n ± 0%  -30.60% (p=0.000 n=20)
AtomicStore64-2   19.61n ± 0%   13.61n ± 0%  -30.57% (p=0.000 n=20)
AtomicStore64-4   19.62n ± 0%   13.61n ± 0%  -30.63% (p=0.000 n=20)
AtomicStore       19.61n ± 0%   13.61n ± 0%  -30.60% (p=0.000 n=20)
AtomicStore-2     19.62n ± 0%   13.61n ± 0%  -30.63% (p=0.000 n=20)
AtomicStore-4     19.62n ± 0%   13.62n ± 0%  -30.58% (p=0.000 n=20)
AtomicStore8      19.61n ± 0%   20.01n ± 0%   +2.04% (p=0.000 n=20)
AtomicStore8-2    19.62n ± 0%   20.02n ± 0%   +2.01% (p=0.000 n=20)
AtomicStore8-4    19.61n ± 0%   20.02n ± 0%   +2.09% (p=0.000 n=20)
geomean           19.61n        15.48n       -21.08%

goos: linux
goarch: loong64
pkg: internal/runtime/atomic
cpu: Loongson-3A6000 @ 2500.00MHz
                |  bench.old  |              bench.new              |
                |   sec/op    |   sec/op     vs base                |
AtomicStore64     18.03n ± 0%   12.81n ± 0%  -28.93% (p=0.000 n=20)
AtomicStore64-2   18.02n ± 0%   12.81n ± 0%  -28.91% (p=0.000 n=20)
AtomicStore64-4   18.01n ± 0%   12.81n ± 0%  -28.87% (p=0.000 n=20)
AtomicStore       18.02n ± 0%   12.81n ± 0%  -28.91% (p=0.000 n=20)
AtomicStore-2     18.01n ± 0%   12.81n ± 0%  -28.87% (p=0.000 n=20)
AtomicStore-4     18.01n ± 0%   12.81n ± 0%  -28.87% (p=0.000 n=20)
AtomicStore8      18.01n ± 0%   12.81n ± 0%  -28.87% (p=0.000 n=20)
AtomicStore8-2    18.01n ± 0%   12.81n ± 0%  -28.87% (p=0.000 n=20)
AtomicStore8-4    18.01n ± 0%   12.81n ± 0%  -28.87% (p=0.000 n=20)
geomean           18.01n        12.81n       -28.89%

[1]: https://loongson.github.io/LoongArch-Documentation/LoongArch-ELF-ABI-EN.html
[2]: https://gcc.gnu.org/git/?p=gcc.git;a=blob_plain;f=gcc/config/loongarch/sync.md

Change-Id: I4ae5e8dd0e6f026129b6e503990a763ed40c6097
Reviewed-on: https://go-review.googlesource.com/c/go/+/581356
Reviewed-by: sophie zhao <zhaoxiaolin@loongson.cn>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Qiqi Huang <huangqiqi@loongson.cn>
Reviewed-by: Meidan Li <limeidan@loongson.cn>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: David Chase <drchase@google.com>