sh: Hook up ERR/PERR/SERR detection for SH7780 PCI host controllers.

These were never handled before, so implement some common infrastructure
to support them, then make use of that in the SH7780-specific code. In
practice there is little here that can not be generalized for SH4 parts,
which will be an incremental change as the 7780/7751 code is gradually
unified.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>