powerpc/64: Remove unused paca->soft_enabled

powerpc/64: Remove unused paca->soft_enabled

In commit 4e26bc4a4ed6 ("powerpc/64: Rename soft_enabled to
irq_soft_mask") we renamed paca->soft_enabled. But then in commit
8e0b634b1327 ("powerpc/64s: Do not allocate lppaca if we are not
virtualized") we added it back. Oops. This happened because the two
patches were in flight at the same time and rebased vs each other
multiple times, and we missed it in review.

Fixes: 8e0b634b1327 ("powerpc/64s: Do not allocate lppaca if we are not virtualized")
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>