[AMDGPU] Fix some tests that did not specify -mcpu

Summary:
This fixes some tests that did not specify -mcpu. Doing that disables
all subtarget features, which gives behavior that (a) does not
necessarily correspond to any actual target, and (b) can change as we
add new subtarget features.

Also added gfx1010 to memtime test.

Differential Revision: https://reviews.llvm.org/D74594

Change-Id: I8c0fe4fa03e9a93ef8bb722cd42d22e064526309