ACPI: remove locking from PM1x_STS register reads

PM1a_STS and PM1b_STS are twins that get OR'd together
on reads, and all writes are repeated to both.

The fields in PM1x_STS are single bits only,
there are no multi-bit fields.

So it is not necessary to lock PM1x_STS reads against
writes because it is impossible to read an intermediate
value of a single bit.  It will either be 0 or 1,
even if a write is in progress during the read.
Reads are asynchronous to writes no matter if a lock
is used or not.

Signed-off-by: Len Brown <len.brown@intel.com>