serial: sh-sci: Introduced function pointers

serial: sh-sci: Introduced function pointers

The aim here is to prepare support for new sci controllers like
the T2H/RSCI whose registers are too much different for being
handled in common code.

This named serial controller also has 32 bits register,
so some return types had to be changed.

The needed generic functions are no longer static, with prototypes
defined in sh-sci-common.h so that they can be used from specific
implementation in a separate file, to keep this driver as little
changed as possible.

For doing so, a set of 'ops' is added to struct sci_port.

Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Thierry Bultel <thierry.bultel.yh@bp.renesas.com>
Link: https://lore.kernel.org/r/20250403212919.1137670-9-thierry.bultel.yh@bp.renesas.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>