google/grunt: Override BayHub EMMC driving strength

Careena EVT SanDisk EMMC sku has high fail rate of 0x5B reboot failure.
It'll need to increase 1.8V EMMC CLK/CMD, Data driving strength for
this issue.

CLK[6:4]
CMD,DATA[3:1]

original register value: 0x6B
enhanced: 0x7F

BUG=b:111964336
BRANCH=master
TEST=emerge-grunt coreboot
Change-Id: I3db38ff12c566c258895c6643008a0472ca528bb
Signed-off-by: Kevin Chiu <Kevin.Chiu@quantatw.com>
Reviewed-on: https://review.coreboot.org/27816
Reviewed-by: Martin Roth <martinroth@google.com>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
3 files changed