intel: Define `RCBA_LENGTH` in Kconfig and use it

Change-Id: Ief81d49f04c1743b2a37633c4a35da9d6ddb0974
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/50039
Reviewed-by: Nico Huber <nico.h@gmx.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
diff --git a/src/southbridge/intel/bd82x6x/acpi/pch.asl b/src/southbridge/intel/bd82x6x/acpi/pch.asl
index 8833a5e..5a80ab0 100644
--- a/src/southbridge/intel/bd82x6x/acpi/pch.asl
+++ b/src/southbridge/intel/bd82x6x/acpi/pch.asl
@@ -181,7 +181,7 @@
 
 
 	// ICH7 Root Complex Register Block. Memory Mapped through RCBA)
-	OperationRegion(RCRB, SystemMemory, CONFIG_FIXED_RCBA_MMIO_BASE, 0x4000)
+	OperationRegion(RCRB, SystemMemory, CONFIG_FIXED_RCBA_MMIO_BASE, CONFIG_RCBA_LENGTH)
 	Field(RCRB, DWordAcc, Lock, Preserve)
 	{
 		Offset(0x0000), // Backbone