dts: bindings: mark power gpio in bg95 as optional

The Quectel BG95 binding currently marks mdm-power-gpios as
required.  This fits designs that expose the PWRKEY pin, but the
BG95-M3 in Mini PCIe form-factor boots automatically via its
on-module “Automatic Power-On Circuit” and does not route
PWRKEY to the card edge.

Signed-off-by: Van Petrosyan <[email protected]>

Author: petrosyan-van

dts/bindings/modem/quectel,bg95.yaml

@@ -10,4 +10,3 @@ include: uart-device.yaml
 properties:
   mdm-power-gpios:
     type: phandle-array
-    required: true