Fix checksum calculation both in romstage and ramstage.

Fix checksum calculation both in romstage and ramstage.

The earlier fix for CMOS checksums only fixed the function rtc_set_checksum,
which would fix the checksum, but then coreboot would no longer honor the
settings because it assumed the checksum is wrong after this.
This change fixes the remaining functions.

Change-Id: I3f52d074df29fc29ae1d940b3dcec3aa2cfc96a5
Signed-off-by: Stefan Reinauer <reinauer@google.com>
Reviewed-on: http://review.coreboot.org/342
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <patrick@georgi-clan.de>