soc/amd/common/espi_util: espi_std_io_decode: fix edge case bug

When address and data register for the SIO control register access is
passed as one I/O region with a size of 2, the corresponding special
decode enable register should be used instead of a generic one to save
the rather limited generic ones for other decode ranges.

Change-Id: Ie54ff6afa2bd2156f7b3a3cf83091f1f932b6993
Signed-off-by: Felix Held <felix-coreboot@felixheld.de>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/44351
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Furquan Shaikh <furquan@google.com>

src/soc/amd/common/block/lpc/espi_util.c

@@ -104,6 +104,9 @@ static int espi_get_unused_io_window(void)
  */
 static int espi_std_io_decode(uint16_t base, size_t size)
 {
+	if (size == 2 && base == 0x2e)
+		return ESPI_DECODE_IO_0X2E_0X2F_EN;
+
 	if (size != 1)
 		return -1;