Introduce iosapic_{read,write,eoi} to hide the IOSAPIC REG_SELECT
stuff.  i386 and x86_64 already do this for io_apic_{read,write}.
Signed-off-by: Bjorn Helgaas <bjorn.helgaas@hp.com>
Signed-off-by: David Mosberger <davidm@hpl.hp.com>