arm/acpi: Add Server Base System Architecture UART support

arm/acpi: Add Server Base System Architecture UART support

The ARM Server Base System Architecture describes a generic UART
interface. It doesn't support clock control registers, modem
control, DMA and hardware flow control features. So, extend the
driver probe() to handle SBSA interface and skip the accessing
PL011 registers that are not described in SBSA document
(ARM-DEN-0029 Version 3.0, 6 APPENDIX B: GENERIC UART).

Signed-off-by: Shanker Donthineni <shankerd@codeaurora.org>
Reviewed-by: Julien Grall <julien.grall@arm.com>
Signed-off-by: Stefano Stabellini <sstabellini@kernel.org>