imx: imx7d-sdb: prepare to synchronise device trees with linux

As a preparatory step remove the epdc reference which does not exist in
the Linux upstream device tree and 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/.imx7d-sdb-qspi.dtb.pre.tmp:10.1-6 Label or path
 epdc not found
+Error: arch/arm/dts/.imx7d-sdb-qspi.dtb.pre.tmp:29.1-7 Label or path
 qspi1 not found
+Error: arch/arm/dts/imx7d-sdb-qspi-u-boot.dtsi:6.1-7 Label or path
 qspi1 not found

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