parisc: Cleanup mmap implementation regarding color alignment

This change simplifies the randomization of file mapping regions. It
reworks the code to remove duplication. The flow is now similar to
that for mips. Finally, we consistently use the do_color_align variable
to determine when color alignment is needed.

Tested on rp3440.

Signed-off-by: John David Anglin <dave.anglin@bell.net>
Signed-off-by: Helge Deller <deller@gmx.de>