sim: arm: add support for MOVW and MOVT instructions

From: Jayant R. Sonar <Jayant.Sonar@kpitcummins.com>

This patch adds simulator support for handling the armv7 instructions
'movw (immediate)' and 'movt'.

Compiler frequently use these instructions to load the 32bit addresses of
global variables, string pointers etc. into the general registers.

In absence of support of these instructions:
1. GDB run simulator fails to print even simple "hello world" string
   on console.
2. Loading of global variable addresses into the registers fail causing
   arithmetic operation failures.

Patch has been regression tested for arm-none-eabi (-march=armv7-a).