sh: sh772[34]: Set serial port sampling rate to 8 for SCIFA ports

SCIFA ports on sh7723 and sh7724 seem to use a sampling rate of half the
value specified in the datasheet. This is currently handled by a custom
baud rate calculation algorithm. The algorithm ID will be removed from
platform data, set the sampling rate directly instead.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>