[ARM] Mark a bunch of .td Operands with type _MEMORY.

This shouldn't affect anything in-tree, as the OperandType users are
mostly smart disassemblers and such; more information is helpful there.
However, on the flip side, that + the fact that this is just hinting at
the meaning of operands makes this not really test-worthy or testable.

Differential Revision: http://reviews.llvm.org/D8620

llvm-svn: 234350