[MCA] Fix wrong definition of ResourceUnitMask in DefaultResourceStrategy.

Field ResourceUnitMask was incorrectly defined as a 'const unsigned' mask. It
should have been a 64 bit quantity instead. That means, ResourceUnitMask was
always implicitly truncated to a 32 bit quantity.
This issue has been found by inspection. Surprisingly, that bug was latent, and
it never negatively affected any existing upstream targets.

This patch fixes  the wrong definition of ResourceUnitMask, and adds a bunch of
extra debug prints to help debugging potential issues related to invalid
processor resource masks.

llvm-svn: 350820