Let t2LDRBi8 and t2LDRBi12 have same Base Pointer

When determining if two different loads are from the same base address,
this patch allows one load to use a t2LDRi8 address mode and another to
use a t2LDRi12 address mode. The current implementation is very
conservative and this allows the case of differing Thumb2 byte loads to
be considered. Allowing these differing modes instead of forcing the exact
same opcode is useful for situations where one opcodes loads from a base
address+1 and a second opcode loads for a base address-1.

Patch by Daniel Stewart.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@188385 91177308-0d34-0410-b5e6-96231b3b80d8