uart: pass register width in the coreboot table

Some SOCs (like pistachio, for instance) provide an 8250 compatible
UART, which has the same register layout, but mapped to a bus of a
different width.

Instead of adding a new driver for these controllers, it is better to
have coreboot report UART register width to libpayload, and have it
adjust the offsets accordingly when accessing the UART.

BRANCH=none
BUG=chrome-os-partner:31438
TEST=with the rest of the patches integrated depthcharge console messages
     show up when running on the FPGA board

Change-Id: I30b742146069450941164afb04641b967a214d6d
Signed-off-by: Patrick Georgi <pgeorgi@chromium.org>
Original-Commit-Id: 2c30845f269ec6ae1d53ddc5cda0b4320008fa42
Original-Change-Id: Ia0a37cd5f24a1ee4d0334f8a7e3da5df0069cec4
Original-Signed-off-by: Vadim Bendebury <vbendeb@chromium.org>
Original-Reviewed-on: https://chromium-review.googlesource.com/240027
Original-Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: http://review.coreboot.org/9738
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <pgeorgi@google.com>

src/include/boot/coreboot_tables.h

@@ -159,6 +159,7 @@ struct lb_serial {
 	uint32_t type;
 	uint32_t baseaddr;
 	uint32_t baud;
+	uint32_t regwidth;
 };
 
 #define LB_TAG_CONSOLE		0x0010