Initializing sensors requires attaching to pd 2. Add an ioctl for that.

This corresponds to FASTRPC_INIT_ATTACH_SENSORS in the downstream driver.
Signed-off-by: Jonathan Marek <jonathan@marek.ca>
Link: https://lore.kernel.org/r/20200908131013.19630-4-jonathan@marek.caSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>