Add support for the new Arm Generic UART _HID

Historically the ACPI _HID for both the Arm PL011 and Generic UARTs
was ARMH0011. In the Arm Base Boot Requirements 2.0 the Generic UART
_HID is changed to ARMHB000. Use this new value in the PL011 driver
where we support both UART types.

This has been observed in some recent EDK2 builds.

Sponsored by: Arm Ltd