RTC: Enable extended CMOS in the bootblock

This makes it available early in romstage without having to
worry when the different romstagse enable it.

Check for extended CMOS to be enabled in early romstage.

This is used by a later commit which uses the extended
CMOS region for stoage.

Change-Id: I9e026d48499c63d6503c2b020d4cc3047126fa93
Signed-off-by: Duncan Laurie <dlaurie@chromium.org>
Reviewed-on: http://review.coreboot.org/1306
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <patrick@georgi-clan.de>

src/southbridge/intel/bd82x6x/bootblock.c

@@ -72,4 +72,7 @@ static void bootblock_southbridge_init(void)
 #endif
 	enable_spi_prefetch();
 	enable_port80_on_lpc();
+
+	/* Enable upper 128bytes of CMOS */
+	RCBA32(RC) = (1 << 2);
 }