libpayload: Add minimal support for PL011 UART

This creates a new PL011 config variable which avoids the
infinite busy wait on serial_putchar() because the register
mapping is not compatible with current implementation.

BUG=None
BRANCH=none
TEST=printf() works on the PL011 based ARMv8 foundation model

Change-Id: I9feda35a50a3488fc504d1561444161e0889deda
Signed-off-by: Marcelo Povoa <marcelogp@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/187020
Reviewed-by: David Hendricks <dhendrix@chromium.org>
2 files changed