soc/intel/skylake: restore MCHBAR and DMIBAR programming

Program MCHBAR, DMIBAR, EPBAR, EDRAMBAR and GDXCBAR.
Also program the PAM registers. The system agent was being
programmed in romstage during pre-console initialization, after
moving to C_ENVIRONMENT bootblock this was missing, restoring
the same.

TEST=Build and Boot Kunimitsu

Change-Id: Iaf310cfb83e58eb8d5affb481dfc343f5d45961b
Signed-off-by: Rizwan Qureshi <rizwan.qureshi@intel.com>
Reviewed-on: https://review.coreboot.org/16224
Reviewed-by: Duncan Laurie <dlaurie@chromium.org>
Tested-by: build bot (Jenkins)
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>

src/soc/intel/skylake/romstage/romstage.c

@@ -45,6 +45,9 @@
 /* SOC initialization before RAM is enabled */
 void soc_pre_ram_init(struct romstage_params *params)
 {
+	/* Program MCHBAR and DMIBAR */
+	systemagent_early_init();
+
 	/* Prepare to initialize memory */
 	soc_fill_pei_data(params->pei_data);
 }