xen/arm: drivers: scif: Don't overwrite firmware settings

xen/arm: drivers: scif: Don't overwrite firmware settings

Besides the 14MHz external clock, the SCIF might be clocked by an
internal 66MHz clock. If this is the case, the current clock source
selection breaks this configuration. Same for the settings done by
the firmware for data bits, stop bits and parity.

Completely drop this and rely on the settings done by the firmware.

Signed-off-by: Dirk Behme <dirk.behme@de.bosch.com>
Reviewed-by: Julien Grall <julien.grall@arm.com>
Signed-off-by: Stefano Stabellini <sstabellini@kernel.org>