serial: sh-sci: Handle port memory region reservations.

serial: sh-sci: Handle port memory region reservations.

At the moment the request/release_port ops are no-ops with the port
remapping case tied in to the config_port op. This moves the remap logic
in to the request_port, balances it with unmapping in the port release,
and finally takes care of the mem region reservations.

All existing users are of the port autoconf variety, so we follow the
example of other drivers that wrap in to the port request by way of the
config op in the UART_CONFIG_TYPE case.

This is the first step towards fixing up conflicts with multiple users
of the same ports, as currently happens between sh-sci and spi_sh_sci.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>