soc/amd/stoneyridge/southbridge.c: Fix get_index_bit limit check

Limit is the maximum number of bits to be tested, however it's being checked
against the number of bytes of uint32_t. when it should be number of bits.
Create a macro to provide the number of bits, and use it instead of sizeof.

BUG=b:75996437
TEST=Add debug messages to see code passing beyond the check, build and
boot grunt, check that it passed the limit check, remove debug code.

Change-Id: Id1dfda26d789183b346b20c37fec923d996b80db
Signed-off-by: Richard Spiegel <richard.spiegel@silverbackltd.com>
Reviewed-on: https://review.coreboot.org/27162
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Martin Roth <martinroth@google.com>

src/soc/amd/stoneyridge/include/soc/southbridge.h

@@ -355,6 +355,7 @@
 
 #define PM1_LIMIT			16
 #define GPE0_LIMIT			28
+#define TOTAL_BITS(a)			(8 * sizeof(a))
 
 /* Bit definitions for MISC_MMIO_BASE register GPPClkCntrl */
 #define GPP_CLK_CNTRL			0

src/soc/amd/stoneyridge/southbridge.c

@@ -696,7 +696,7 @@ static int get_index_bit(uint32_t value, uint16_t limit)
 	uint16_t i;
 	uint32_t t;
 
-	if (limit >= sizeof(uint32_t))
+	if (limit >= TOTAL_BITS(uint32_t))
 		return -1;
 
 	/* get a mask of valid bits. Ex limit = 3, set bits 0-2 */