of/irq: Move irq_of_parse_and_map() to common code
Merge common code between PowerPC and Microblaze. SPARC implements
irq_of_parse_and_map(), but the implementation is different, so it
does not use this code.
Signed-off-by: Grant Likely <grant.likely@secretlab.ca> Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Michal Simek <monstr@monstr.eu> Cc: "David S. Miller" <davem@davemloft.net> Cc: Stephen Rothwell <sfr@canb.auug.org.au> Cc: Jeremy Kerr <jeremy.kerr@canonical.com>