intel: Turn `DEFAULT_RCBA` into a Kconfig symbol

Create `FIXED_RCBA_MMIO_BASE` and use it everywhere, except in cases
where a pointer cast would be necessary. Instances in Sandy Bridge MRC
code were left as-is intentionally, so as not to collide with another
cleanup patch train.

Tested with BUILD_TIMELESS=1, these boards remain identical:
- Asus P8Z77-V LX2
- Packard Bell MS2290

Change-Id: I642958fbd6f02dbf54812d6a75d6bc3087acc77a
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/50036
Reviewed-by: Nico Huber <nico.h@gmx.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
diff --git a/src/southbridge/intel/lynxpoint/lpc.c b/src/southbridge/intel/lynxpoint/lpc.c
index 24a5a7e..20b9b43 100644
--- a/src/southbridge/intel/lynxpoint/lpc.c
+++ b/src/southbridge/intel/lynxpoint/lpc.c
@@ -557,9 +557,9 @@
 	res->flags = IORESOURCE_MEM | IORESOURCE_ASSIGNED | IORESOURCE_FIXED;
 
 	/* RCBA */
-	if ((uintptr_t)DEFAULT_RCBA < default_decode_base) {
+	if (CONFIG_FIXED_RCBA_MMIO_BASE < default_decode_base) {
 		res = new_resource(dev, RCBA);
-		res->base = (resource_t)(uintptr_t)DEFAULT_RCBA;
+		res->base = (resource_t)CONFIG_FIXED_RCBA_MMIO_BASE;
 		res->size = 16 * 1024;
 		res->flags = IORESOURCE_MEM | IORESOURCE_ASSIGNED |
 			     IORESOURCE_FIXED | IORESOURCE_RESERVE;