R600/SI: Add more special cases for opcodes to ensureSRegLimit()

Also factor out the register class lookup to its own function.
R600/SI: Use VSrc_* register classes as the default classes for types

Since the VSrc_* register classes contain both VGPRs and SGPRs, copies
that used be emitted by isel like this:

SGPR = COPY VGPR

Will now be emitted like this:

VSrC = COPY VGPR

This patch also adds a pass that tries to identify and fix situations where
a VGPR to SGPR copy may occur.  Hopefully, these changes will make it
impossible for the compiler to generate illegal VGPR to SGPR copies.
[mips] Rename register classes CPURegs and CPU64Regs.
Test to see if logging is enabled before printing
to a log channel in StopInfoBreakpoint::PerformAction().
<rdar://problem/14651751>