The following moves the creation of IPR interupts into setup-7750.c
and updates a few other things to make it all work after the "Drop
CPU subtype IRQ headers" commit. It boots and runs fine on my titan
board.

 - adds an ipr_idx to the ipr_data and uses a function in the subtype
   code to calculate the address of the IPR registers

 - adds a function to enable individual interrupt mode for externals
   in the subtype code and calls that from the titan board code
   instead of doing it directly.

 - I changed the shift in the ipr_data to be the actual # of bits to
   shift, instead of the numnber / 4 - made it easier to match with
   the manual.
Signed-off-by: NJamie Lenehan <lenehan@twibble.org>
Signed-off-by: NPaul Mundt <lethal@linux-sh.org>