nb/intel/i945/early_init.c: Replace numbers with macros

Change-Id: I270d17a2eff2c6664bf936425a6ed344be3feabe
Signed-off-by: Elyes HAOUAS <ehaouas@noos.fr>
Reviewed-on: https://review.coreboot.org/21524
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Nico Huber <nico.h@gmx.de>
Reviewed-by: Sumeet R Pawnikar <sumeet.r.pawnikar@intel.com>

src/northbridge/intel/i945/early_init.c

@@ -175,7 +175,7 @@ static void i945_setup_bars(void)
 	printk(BIOS_DEBUG, " done.\n");
 
 	/* Enable upper 128bytes of CMOS */
-	RCBA32(0x3400) = (1 << 2);
+	RCBA32(RC) = (1 << 2);
 
 	printk(BIOS_DEBUG, "Setting up static northbridge registers...");
 	/* Set up all hardcoded northbridge BARs */