[AArch64][GlobalISel] Don't bail out of the select(cmp(a, b)) -> csel...

[AArch64][GlobalISel] Don't bail out of the select(cmp(a, b)) -> csel optimization with multiple users.

It can still be beneficial to do the optimization if the result of the compare
is used by *another* select.

Differential Revision: https://reviews.llvm.org/D73511