powerpc/64: Remove unused paca->soft_enabled

powerpc/64: Remove unused paca->soft_enabled

In commit 2011b724289e ("powerpc/64: Rename soft_enabled to
irq_soft_mask") we renamed paca->soft_enabled. But then in commit
37611d20651c ("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: 37611d20651c ("powerpc/64s: Do not allocate lppaca if we are not virtualized")
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>