arm64: dts: marvell: armada-37xx: add device node for UART clock and use it

arm64: dts: marvell: armada-37xx: add device node for UART clock and use it

Define DT node for UART clock "marvell,armada-3700-uart-clock" and use
this UART clock as a base clock for all UART devices.

Reviewed-by: Marek Behún <kabel@kernel.org>
Acked-by: Gregory CLEMENT <gregory.clement@bootlin.com>
Signed-off-by: Pali Rohár <pali@kernel.org>
Signed-off-by: Marek Behún <kabel@kernel.org>
Link: https://lore.kernel.org/r/20220219152818.4319-7-kabel@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>