This fixes three issues related to Thumb literal loads:

1. The offset range for Thumb1 PC relative loads is [0..1020] and not [-1024..1020]
2. Thumb2 PC relative loads may define the PC, so the restriction placed on target register is removed
3. Removes unneeded alias between "ldr.n" and t1LDRpci. ".n" is actually stripped by both tablegen
and the ASM parser, so this alias rule really does nothing


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@188466 91177308-0d34-0410-b5e6-96231b3b80d8
Drive-by fix for a doxygen comment in MachineInstr.h.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@188467 91177308-0d34-0410-b5e6-96231b3b80d8