arm64: dts: renesas: eagle: Add x1 clock

This adds X1 clock which supplies a frequency of 148.5 MHz.
This clock is connected to the external dot clock input signal.

Signed-off-by: Valentine Barshak <valentine.barshak@cogentembedded.com>
[geert: Verified schematics]
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Tested-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
Link: https://lore.kernel.org/r/75a66bae21937da1c69e8024ce61b35aad4ac9b8.1620119570.git.geert+renesas@glider.be