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coreboot supports an in-memory console to store firmware logs even when
no serial console is available. It is widely supported by
coreboot-compatible bootloaders (including SeaBIOS and GRUB) and can be
read by the Linux kernel.

This patch allows BL31 to add its own log messages to this console. The
driver will be registered automatically if coreboot support is compiled
in and detects the presence of a console buffer in the coreboot tables.

Change-Id: I31254dfa0c2fdeb7454634134b5707b4b4154907
Signed-off-by: Julius Werner <jwerner@chromium.org>

This patch adds the foundation for a platform-independent coreboot
support library that can be shared by all platforms that boot BL31 from
coreboot (acting as BL2). It adds code to parse the "coreboot table", a
data structure that coreboot uses to communicate different kinds of
information to later-stage firmware and certain OS drivers.

As a first small use case for this information, allow platforms to
access the serial console configuration used by coreboot, removing the
need to hardcode base address and divisors and allowing Trusted Firmware
to benefit from coreboot's user configuration (e.g. which UART to pick
and which baud rate to use).

Change-Id: I2bfb39cd2609ce6640b844ab68df6c9ae3f28e9e
Signed-off-by: Julius Werner <jwerner@chromium.org>