nrf: add support for UICR configuration.

- APPROTECT enable/disable. Notably this fixes issues with nrf52-rev3 and nrf53 from locking itself at reset.
- Use NFC pins as GPIO.
- Use RESET pin as GPIO.

NFC and RESET pins singletons are made available only when usable as GPIO,
for compile-time checking.

embassy-nrf/src/chips/nrf52820.rs

@@ -6,6 +6,8 @@ pub const FORCE_COPY_BUFFER_SIZE: usize = 512;
 
 pub const FLASH_SIZE: usize = 256 * 1024;
 
+pub const RESET_PIN: u32 = 18;
+
 embassy_hal_common::peripherals! {
     // USB
     USBD,
@@ -106,6 +108,7 @@ embassy_hal_common::peripherals! {
     P0_15,
     P0_16,
     P0_17,
+    #[cfg(feature="reset-pin-as-gpio")]
     P0_18,
     P0_19,
     P0_20,
@@ -168,6 +171,7 @@ impl_pin!(P0_14, 0, 14);
 impl_pin!(P0_15, 0, 15);
 impl_pin!(P0_16, 0, 16);
 impl_pin!(P0_17, 0, 17);
+#[cfg(feature = "reset-pin-as-gpio")]
 impl_pin!(P0_18, 0, 18);
 impl_pin!(P0_19, 0, 19);
 impl_pin!(P0_20, 0, 20);