flash_ec: make c2d2 uart flashing more reliable
flash_ec: make c2d2 uart flashing more reliable

Remove sleeps from C2D2 flash path and ensure the EC doesn't come out of
reset long enough to do damage before we start flashing it.

BRANCH=none
BUG=b:150796623
TEST=Verify that no console prints from EC occur before flashing happens
(this is a positive change in behavior with this CL)

Cq-Depend: chromium:2090124, chromium:2090576
Signed-off-by: Jett Rink <9d4aef0593e6843318d99df31597fb6153b89787@chromium.org>
Change-Id: I76560dcb6e7483ae36dc8c0f37ef99da126b0be3
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/2090077
Reviewed-by: David Schneider <f6dc7060de10912bba612c52f98c21c17bd19e92@chromium.org>
Reviewed-by: Raul E Rangel <9a9c998e11a2655b1de9a05eeeef5f710c0dc7ed@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec