[AArch64][GlobalISel] Enable memcpy family combines on minsize functions
The combines in tryCombineMemCpyFamily have heuristics (e.g.
TLI.getMaxStoresPerMemset) which consider size. So, theoretically, enabling
these combines on minsize functions shouldn't be harmful.
With this enabled we save 0.9% geomean on CTMark at -Oz, and 5.1% on Bullet.
There are no code size regressions.
Differential Revision: https://reviews.llvm.org/D102198