amd/stoneyridge: Add function to find PmControl register

Find the PmControl register's I/O address by checking the hardware in
PMx62.  Don't rely on the address being the coreboot default.  PmControl
is the first register in the AcpiPm1CntBlk.

Change-Id: Ibb608dcaa7801af067d6edd86f92c117c2ac08a6
Signed-off-by: Marshall Dawson <marshalldawson3rd@gmail.com>
Reviewed-on: https://review.coreboot.org/21882
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-by: Marc Jones <marc@marcjonesconsulting.com>

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

@@ -202,6 +202,7 @@ u16 smi_read16(u8 reg);
 u32 smi_read32(u8 reg);
 void smi_write16(u8 reg, u16 value);
 void smi_write32(u8 reg, u32 value);
+uint16_t pm_acpi_pm_cnt_blk(void);
 int s3_load_nvram_early(int size, u32 *old_dword, int nvram_pos);
 void s3_resume_init_data(void *FchParams);
 int s3_save_nvram_early(u32 dword, int size, int  nvram_pos);

src/soc/amd/stoneyridge/sb_util.c

@@ -64,3 +64,8 @@ void smi_write16(uint8_t offset, uint16_t value)
 {
 	write16((void *)(APU_SMI_BASE + offset), value);
 }
+
+uint16_t pm_acpi_pm_cnt_blk(void)
+{
+	return pm_read16(PM1_CNT_BLK);
+}