powerpc: Convert the MPIC MSI code to use msi_bitmap

This affects the U3 MSI code as well as the PASEMI MSI code.  We keep
some of the MPIC routines as helpers, and also the U3 best-guess
reservation logic.  The rest is replaced by the generic code.

And a few printk format changes due to hwirq type change.

Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Paul Mackerras <paulus@samba.org>