cr50: Replace "cr50" to "GSC" in debug messages

cr50: Replace "cr50" to "GSC" in debug messages

The cr50.c file currently prints "cr50" in debug messages no
matter the system is using Cr50 or Ti50. This can be confusing
for developers.

This patch replaces "cr50" with "GSC" in debug messages. Using
"GSC" makes the messages more clear and easier to search via
`grep`.

BUG=none
TEST=Build and test on karis

Change-Id: I21f66cf8b608ca4e4dc82d7a55a851ec996c8bb3
Signed-off-by: Tyler Wang <tyler.wang@quanta.corp-partner.google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/82420
Reviewed-by: Eric Lai <ericllai@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Yu-Ping Wu <yupingso@google.com>
Reviewed-by: Jon Murphy <jpmurphy@google.com>