LivePhysRegs/IfConversion: Change some types from unsigned to MCPhysReg; NFC

Change the type in a couple of lists and sets that only store physical
registers from unsigned to MCPhysRegs. The later is only 16bits and
saves us a bit of memory.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@346254 91177308-0d34-0410-b5e6-96231b3b80d8
7 files changed