Add SYS_SUPPORTS_ZBOOT and SYS_SUPPORTS_ZBOOT_UART16550 config options
for XLR and XLP.

Update boot/compressed/uart-16550.c to add UART port for XLR and XLP.
Signed-off-by: Jayachandran C <jchandra@broadcom.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/5417/Signed-off-by: Ralf Baechle <ralf@linux-mips.org>