[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