realtek_mst_i2c_spi.c: Define some register names

Try to document some of the register magics with plausible
names for readability.

BUG=b:152558985,b:148745673
BRANCH=none
TEST=builds

Change-Id: I97313f6f14438e4cbfc62faa7242cf6fc271f387
Signed-off-by: Edward O'Callaghan <quasisec@google.com>
Reviewed-on: https://review.coreboot.org/c/flashrom/+/41022
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
1 file changed