powerpc/irq: Add helper to set regs->softe

powerpc/irq: Add helper to set regs->softe

[ Upstream commit fb5608fd117a8b48752d2b5a7e70847c1ed33d33 ]

regs->softe doesn't exist on PPC32.

Add irq_soft_mask_regs_set_state() helper to set regs->softe.
This helper will void on PPC32.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/5f37d1177a751fdbca79df461d283850ca3a34a2.1612796617.git.christophe.leroy@csgroup.eu
Signed-off-by: Sasha Levin <sashal@kernel.org>