[ARM] Fix entire dcache operations on ARMv7 CPUs

The original ARM_ENTIER_DCACHE_OP() macro accessed r10 and r11 register which
were not saved and restored. As a result, whenever entier dcache operations
were called the r10 & r11 got corrupted hence crashing Xvisor.

The patch fixes the above described issue.

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