Merged hw_irq.h between ppc32 & ppc64.  Added support to use the Book-E
wrtee[i] instructions that allow modifying MSR[EE] atomically.
Additionally, added get_irq_desc() macros to ppc32 to allow mask_irq(),
unmask_irq(), and ack_irq() to be common between ppc32 & ppc64.

Note: because 64-bit Book-E implementations only have a 32-bit MSR the
macro's for Book-E need to come before the PPC64 macro's to ensure the
right thing happends for 64-bit Book-E processors.
Signed-off-by: Kumar Gala <kumar.gala@freescale.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>