imx8mp levy: add B79/MV bootselect/clear-button support

This patch adds support for reading the state of the
bootselect/clear-all button on ModularVision/B79 baseboards (via SMARC
GPIO7)

Tested and working on both ModularVision and B79

board/keithkoep/common/baseboard.c

@@ -31,9 +31,9 @@ const static board_info_t baseboards[] = {
     // boot pin: GPIO4_IO09, SODIMM 71
 	{BT_PBB,            "pbb",          false,  "105",  false,  PFID_REVISION_TYPE_SOM_NORMAL },
 
-    // boot pin: SMARC_GPIO7 (I2C GPIO-Expander GPIO7) =>167?
-	{BT_B79,            "CSM-B79",          false,  "0",  false,  PFID_REVISION_TYPE_SMARC },
-	{BT_MODULARVISION,  "ModularVision",    false,  "0",  false,  PFID_REVISION_TYPE_SMARC },
+    // boot pin: SMARC_GPIO7 => PCAL6416 P0_5 => U-Boot "gpio@20_5" => U-Boot gpio no. 165)
+	{BT_B79,            "CSM-B79",          false,  "165",  false,  PFID_REVISION_TYPE_SMARC },
+	{BT_MODULARVISION,  "ModularVision",    false,  "165",  false,  PFID_REVISION_TYPE_SMARC },
 
 	{BT_MX6_NALLINO, "Nallino", true, "0", true, PFID_REVISION_TYPE_SBC_IMX6_INVERTED},
 	{BT_MX6_SANTARO, "Santaro", true, "0", true, PFID_REVISION_TYPE_SBC_IMX6_INVERTED},