gpu: ipu-v3: make const arrays int_reg static, shrinks object size

Don't populate the const read-only arrays int_reg on the stack but instead
make them static. Makes the object code smaller by over 80 bytes:

Before:
   text	   data	    bss	    dec	    hex	filename
  28024	   8936	    192	  37152	   9120	drivers/gpu/ipu-v3/ipu-common.o

After:
   text	   data	    bss	    dec	    hex	filename
  27794	   9080	    192	  37066	   90ca	drivers/gpu/ipu-v3/ipu-common.o

(gcc version 7.2.0 x86_64)

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>