[THUMB2] add .w suffixes for ldr/str (immediate) T4

The Linux kernel when built with CONFIG_THUMB2_KERNEL makes use of these
instructions with immediate operands and wide encodings.

These are the T4 variants of the follow sections from the Arm ARM.
F5.1.72 LDR (immediate)
F5.1.229 STR (immediate)

I wasn't able to represent these simple aliases using t2InstAlias due to
the Constraints on the non-suffixed existing instructions, which results
in some manual parsing logic needing to be added.

F1.2 Standard assembler syntax fields
describes the use of the .w (wide) vs .n (narrow) encoding suffix.

Link: https://bugs.llvm.org/show_bug.cgi?id=49118
Link: https://github.com/ClangBuiltLinux/linux/issues/1296


Reported-by: Stefan Agner <stefan@agner.ch>
Reported-by: Arnd Bergmann <arnd@kernel.org>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>

Reviewed By: DavidSpickett

Differential Revision: https://reviews.llvm.org/D96632