powerpc/irq: Rework helpers that manipulate MSR[EE/RI]

In preparation of porting PPC32 to C syscall entry/exit,
rewrite the following helpers as static inline functions and
add support for PPC32 in them:
	__hard_irq_enable()
	__hard_irq_disable()
	__hard_EE_RI_disable()
	__hard_RI_enable()

Then use them in PPC32 version of arch_local_irq_disable()
and arch_local_irq_enable() to avoid code duplication.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/0e290372a0e7dc2ae657b4a01aec85f8de7fdf77.1612796617.git.christophe.leroy@csgroup.eu