cpufreq: use work_on_cpu in acpi-cpufreq.c for drv_read and drv_write

cpufreq: use work_on_cpu in acpi-cpufreq.c for drv_read and drv_write

Impact: use new work_on_cpu function to reduce stack usage

Replace the saving of current->cpus_allowed and set_cpus_allowed_ptr() with
a work_on_cpu function for drv_read() and drv_write().

Basically converts do_drv_{read,write} into "work_on_cpu" functions that
are now called by drv_read and drv_write.

Note: This patch basically reverts 50c668d6 which reverted 7503bfba, now
that the work_on_cpu() function is more stable.

Signed-off-by: Mike Travis <[email protected]>
Acked-by: Rusty Russell <[email protected]>
Tested-by: Dieter Ries <[email protected]>
Tested-by: Maciej Rutecki <[email protected]>
Cc: Dave Jones <[email protected]>
Cc: <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>