Add support for analog USBPD on STM32G4xx. (#11824)

* Add support for analog USBPD on STM32G4xx.

* Split up to a list of driver types, allow for custom.

drivers/usbpd.h

@@ -0,0 +1,29 @@
+/* Copyright 2021 Nick Brassel (@tzarc)
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+typedef enum {
+    USBPD_500MA,
+    USBPD_1500MA,
+    USBPD_3000MA,
+} usbpd_allowance_t;
+
+// Initialises the USBPD subsystem
+void usbpd_init(void);
+
+// Gets the current state of the USBPD allowance
+usbpd_allowance_t usbpd_get_allowance(void);