[ARM] arm32: Minor improvements to ARM hypercall instruction emulation

This patch does improvements and cosmetic changes to ARM hypercall
instruction emulation by micro-optimizing functions involved in
hypercall instruction emulation.

This patch achieves an increase of 20-30 DMIPS in Guest Linux and
boot-time reduction of 1-2 seconds for Guest Linux when tested
on QEMU.

Signed-off-by: Anup Patel <anup@brainfault.org>