refactor(plat/arm): use mmio* functions to read/write NVFLAGS registers

Used mmio* functions to read/write NVFLAGS registers to avoid
possibile reordering of instructions by compiler.

Change-Id: Iae50ac30e5413259cf8554f0fff47512ad83b0fd
Signed-off-by: Manish V Badarkhe <Manish.Badarkhe@arm.com>
2 files changed