MIPS: rb532: Fix MMIO UART resource registration

MIPS: rb532: Fix MMIO UART resource registration

Since commit 6e690d54cfa8 ("serial: 8250: fix return error code in
serial8250_request_std_resource()"), registering an 8250 MMIO port
without mapbase no longer works, as the resource range is derived from
mapbase/mapsize.

Populate mapbase and mapsize accordingly. Also drop ugly membase KSEG1
pointer and set UPF_IOREMAP instead, letting the 8250 core perform the
ioremap.

Fixes: 6e690d54cfa8 ("serial: 8250: fix return error code in serial8250_request_std_resource()")
Cc: stable@vger.kernel.org
Reported-by: Waldemar Brodkorb <wbx@openadk.org>
Link: https://lore.kernel.org/linux-mips/aX-d0ShTplHKZT33@waldemar-brodkorb.de/
Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>