[POWERPC] Provide dummy hard_irq_enable/disable() for PPC32

To allow arch/powerpc/kernel/crash.c to build on 32-bit we need a
definition of hard_irq_disable(). 32-bit doesn't support the lazy
interrupt disabling mechanism, so on 32-bit hard_irq_disable() is
simply local_irq_disable(). Add a definition for hard_irq_enable()
just for completeness.

This allows (KEXEC=y && PPC32=y) to build again. Broken since
d04c56f7.

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