MAINTAINERS: Add Kishon as maintainer of PHY bindings

DT bindings normally go in via subsystem maintainers, so add PHY
bindings under generic PHY framework.

Reported-by: Gustavo A. R. Silva <[e-mail]>
Cc: Kishon Vijay Abraham I <[e-mail]>
Signed-off-by: Rob Herring <[e-mail]>
Signed-off-by: Kishon Vijay Abraham I <[e-mail]>

MAINTAINERS

···
 S:	Supported
 F:	drivers/phy/
 F:	include/linux/phy/
+F:	Documentation/devicetree/bindings/phy/
 
 GENERIC PINCTRL I2C DEMULTIPLEXER DRIVER
 M:	Wolfram Sang <[e-mail]>