imx: imx7-cm: prepare to synchronise device trees with linux

As a preparatory step rename the qspi1 reference to qspi as this is how
it is named in the Linux upstream device tree.

This avoids the following error once synchronised:

+Error: arch/arm/dts/.imx7-cm.dtb.pre.tmp:96.1-7 Label or path qspi1 not
 found

Signed-off-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>