mb/google/hatch/var/kohaku: ensure FPMCU is power cycled on reset

mb/google/hatch/var/kohaku: ensure FPMCU is power cycled on reset

Leakage from the SPI CS line onto the FPMCU VDD rail was preventing
the FPMCU from fully shutting down on AP reset.

Instead of simply turning off the power rail, now ensure the CS
line is not driven high until late in coreboot.

This ensures it is completely off for the requisite minimum of 200ms
(now measured at approx 1100ms).

BUG=b:245953688
TEST=Confirmed FPMCU is still functional on Kohaku.
Confirmed FpRebootPowerCycle unit test now passes
BRANCH=Hatch

Signed-off-by: Tarun Tuli <taruntuli@google.com>
Change-Id: I1e7e32f61c3ac1b3154d42821cc1dd4c5d3de303
Reviewed-on: https://review.coreboot.org/c/coreboot/+/68819
Reviewed-by: Nick Vaccaro <nvaccaro@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>