ACPI: Convert wake_sleep_flags to a value instead of function

With commit a2ef5c4fd44ce3922435139393b89f2cce47f576
"ACPI: Move module parameter gts and bfs to sleep.c" the wake_sleep_flags
is required when calling acpi_enter_sleep_state, which means
that if there are functions outside the sleep.c code they
can't get the wake_sleep_flags values.

This converts the function in to a exported value and converts
the module config operands to a function.

Acked-by: Rafael J. Wysocki <rjw@sisk.pl>
Acked-by: Lin Ming <ming.m.lin@intel.com>
[v2: Parameters can be turned on/off dynamically]
[v3: unsigned char -> u8]
[v4: val -> kp->arg]
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Link: http://lkml.kernel.org/r/1335150198-21899-2-git-send-email-konrad.wilk@oracle.com
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>