aarch64: Add PL061 for device tree implementation

This commit adds a new legacy device PL011 for the AArch64 device
tree implementation.

Signed-off-by: Henry Wang <Henry.Wang@arm.com>

arch/src/lib.rs

@@ -129,6 +129,9 @@ pub enum DeviceType {
     /// Device Type: RTC.
     #[cfg(target_arch = "aarch64")]
     RTC,
+    /// Device Type: GPIO.
+    #[cfg(target_arch = "aarch64")]
+    GPIO,
 }
 
 /// Default (smallest) memory page size for the supported architectures.