ACPI: Make FADT entries for RTC/CMOS architectural

For AMD, replace name RTC_ALT_CENTURY with RTC_CLK_ALTCENTURY
that points to same offset. Since the century field inside
RTC falls within the NVRAM space, and could interfere with
OPTION_TABLE, it is now guarded with config USE_PC_CMOS_ALTCENTURY.

There were no reference for the use of offset 0x48 for century.

Change-Id: I965a83dc8daaa02ad0935bdde5ca50110adb014a
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/74601
Reviewed-by: Elyes Haouas <ehaouas@noos.fr>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Felix Held <felix-coreboot@felixheld.de>

src/include/pc80/mc146818rtc.h

@@ -93,6 +93,9 @@
 #define RTC_CLK_YEAR		9
 #define RTC_CLK_ALTCENTURY	0x32
 
+#define RTC_DATE_ALARM		RTC_REG_D
+#define RTC_MONTH_ALARM		0
+
 /* On PCs, the checksum is built only over bytes 16..45 */
 #define PC_CKS_RANGE_START	16
 #define PC_CKS_RANGE_END	45