soc/intel/apollolake: Clean up code by using common System Agent module

This patch currently contains the SA initialization
required for bootblock phase -

1. Use SOC_INTEL_COMMON_BLOCK_SA kconfig for common SA code.
2. Perform PCIEXBAR programming based on soc configurable
    PCIEX_LENGTH_xxxMB
3. Use common systemagent header file.

Change-Id: I01a24e2d4f1c8c9ca113c128bb6b3eac23dc79ad
Signed-off-by: Barnali Sarkar <barnali.sarkar@intel.com>
Signed-off-by: Subrata Banik <subrata.banik@intel.com>
Reviewed-on: https://review.coreboot.org/18567
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Tested-by: build bot (Jenkins)

src/soc/intel/apollolake/memmap.c

@@ -27,7 +27,7 @@
 #include <assert.h>
 #include <cbmem.h>
 #include <device/pci.h>
-#include <soc/northbridge.h>
+#include <soc/systemagent.h>
 #include <soc/pci_devs.h>
 #include <soc/smm.h>