amd/stoneyridge: Use generic fixed MTRR setup

Add the X86_AMD_FIXED_MTRRS select back to Kconfig.  This got lost
when stoneyridge was converted from a cpu/northbridge/southbridge
implementation to soc/.

Remove the setup from model_15_init.c because this is duplicated
functionality.

BUG=b:68019051
TEST=Boot Kahlee, check steps with HDT

Change-Id: Id5526dcff12555efccab811fa3442ba1bff051bb
Signed-off-by: Marshall Dawson <marshalldawson3rd@gmail.com>
Reviewed-on: https://review.coreboot.org/23723
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Marc Jones <marc@marcjonesconsulting.com>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
2 files changed