arm64: dts: salvator-x: Enable SCIF_CLK frequency and pins

Add and enable the external crystal for the SCIF_CLK and its pinctrl, to
be used by the Baud Rate Generator for External Clock (BRG) on (H)SCIF.

This increases the range and accuracy of supported baud rates:
  - SCIF:
      - Supports now 50, 230400, 460800, 500000, and 921600 bps,
      - Perfect match for standard 50-460800, and 9216000 bps.
  - HSCIF:
      - Supports now 50, 75, and 110 bps,
      - Perfect match for standard 50-460800, and 9216000 bps.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>