arm64: dts: Remove unused properties from FSL QSPI driver nodes

The properties 'num-cs' and 'bus-num' were never read by the driver
and can be removed.

Signed-off-by: Frieder Schrempf <frieder.schrempf@kontron.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>