arc: axs10x - add support of ARC PGU

arc: axs10x - add support of ARC PGU

Synopsys DesignWare ARC SDP boards sport ARC SDP display
controller attached to ADV7511 HDMI encoder.

That change adds desctiption of both ARC PGU and ADV7511 in
ARC SDP'd base-board Device Tree.

Signed-off-by: Alexey Brodkin <[email protected]>
Cc: Rob Herring <[email protected]>
Cc: Pawel Moll <[email protected]>
Cc: Mark Rutland <[email protected]>
Cc: Ian Campbell <[email protected]>
Cc: Kumar Gala <[email protected]>
Cc: Vineet Gupta <[email protected]>
Cc: [email protected]
Cc: [email protected]