serial: sh-sci: Add support for RZ/G3E RSCI

serial: sh-sci: Add support for RZ/G3E RSCI

Add support for RZ/G3E RSCI. RSCI IP found on the RZ/G3E SoC is similar
to RZ/T2H, but it has a 32-stage FIFO. It has 6 clocks(5 module clocks
+ 1 external clock) instead of 3 clocks(2 module clocks + 1 external
clock) on T2H, has 6 irqs compared to 4 on RZ/T2H and has multiple resets.
Add support for the hardware flow control.

Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Tested-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Link: https://patch.msgid.link/20251129164325.209213-18-biju.das.jz@bp.renesas.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>