google/snow: Change MMC0 to work in 8 bit mode.

The MMC0 on google/snow can run in 8 bit mode. To simplify driver development,
we thought disabling it (using zero, which runs in 1-bit / 4-bit mode) may help.

However, after some experiments in payload drivers, setting pinmux to 8 bit mode
can still allow MMC to run in 1-bit / 4-bit mode, so it's pretty safe to enable
8 bit mode by default for better performance.

Verified to boot on google/snow, and got MMC0 working.

Change-Id: Ic0acc723fe6a8aecf373429d3801beadd70815d9
Signed-off-by: Ronald G. Minnich <rminnich@gmail.com>
Reviewed-on: http://review.coreboot.org/2585
Tested-by: build bot (Jenkins)
Reviewed-by: David Hendricks <dhendrix@chromium.org>
1 file changed