arm/exynos: Allow releasing UART retention for resume.

The UART / serial console is put in retention state by kernel during suspend /
resume path, which caused Coreboot not able to print any messages during resume.

Sending values to the padret_uart_opt inside PMU may release UART, but that may
also cause unexpected output when kernel is back. However, it's still very
helpful when we are debugging suspend/resume inside Coreboot.

To get UART message on resume, call wakeup_enable_uart() in boot block or
romstage (before console_init).

BUG=none
TEST=emerge-peach_pit chromeos-coreboot-peach_pit

Change-Id: Ib5759cb402c6e018d9dba14fad8b61f6a1b1a265
Reviewed-on: https://chromium-review.googlesource.com/170440
Tested-by: Hung-Te Lin <hungte@chromium.org>
Reviewed-by: Hung-Te Lin <hungte@chromium.org>
Commit-Queue: Hung-Te Lin <hungte@chromium.org>
8 files changed