allwinner: psci: Drop .pwr_domain_pwr_down_wfi callback
allwinner: psci: Drop .pwr_domain_pwr_down_wfi callback

When operating on the local cpu, sunxi_cpu_power_off_self() only "arms"
the ARISC to perform the power-off process; the SCP waits for the CPU to
enter WFI before acutally powering it off. Since this matches the
expected split between .pwr_domain_off and .pwr_domain_pwr_down_wfi, we
can move the sunxi_cpu_power_off_self() call to sunxi_pwr_domain_off().
Since that change makes sunxi_pwr_down_wfi() equivalent to the default
implementation, the callback is no longer needed.

Change-Id: I7d65f66c550d1c69fa5e9945affd7a25b3d3ef42
Signed-off-by: Samuel Holland <c16aab9fe3288df0fb8fc1d24990a300b6b8f299@sholland.org>

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