amd/stoneyridge: Add function to find Pm1EvtBlk base

The AcpiPm1EvtBlk base I/O address is configured in PMx60.  Add a
helper function to read this.  The register is not lockable so it
shouldn't be assumed to be at its original address.

Change-Id: I91ebfb454c2d2ae561e658d903f33bfb34e1ad6f
Signed-off-by: Marshall Dawson <marshalldawson3rd@gmail.com>
Reviewed-on: https://review.coreboot.org/22413
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Marc Jones <marc@marcjonesconsulting.com>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

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

@@ -265,6 +265,7 @@ void smi_write8(uint8_t offset, uint8_t value);
 void smi_write16(uint8_t offset, uint16_t value);
 void smi_write32(uint8_t offset, uint32_t value);
 uint16_t pm_acpi_pm_cnt_blk(void);
+uint16_t pm_acpi_pm_evt_blk(void);
 int s3_load_nvram_early(int size, u32 *old_dword, int nvram_pos);
 int s3_save_nvram_early(u32 dword, int size, int  nvram_pos);
 void bootblock_fch_early_init(void);

src/soc/amd/stoneyridge/sb_util.c

@@ -79,3 +79,8 @@ uint16_t pm_acpi_pm_cnt_blk(void)
 {
 	return pm_read16(PM1_CNT_BLK);
 }
+
+uint16_t pm_acpi_pm_evt_blk(void)
+{
+	return pm_read16(PM_EVT_BLK);
+}