allwinner: a64: power: Make sunxi_turn_off_soc static
allwinner: a64: power: Make sunxi_turn_off_soc static

The function is only used in this file, and it doesn't make sense for it
to be used anywhere else.

Signed-off-by: Samuel Holland <c16aab9fe3288df0fb8fc1d24990a300b6b8f299@sholland.org>
Change-Id: Iab18f082911edcdbc37ceeaff8c512be68e0cb0f

achingupta/arm-trusted-firmware,achingupta/arm-trusted-firmware