Add an implementation of the array_index_mask_nospec() function for
mitigating Spectre variant 1 throughout the kernel.
Signed-off-by: NRussell King <rmk+kernel@armlinux.org.uk>
Acked-by: NMark Rutland <mark.rutland@arm.com>
Boot-tested-by: NTony Lindgren <tony@atomide.com>
Reviewed-by: NTony Lindgren <tony@atomide.com>