kernel: rng: Add IOCTL support to disable bus bandwidth

QRNG bus scale is set to high before qrng_read & set to
low after qrng_read, this impacts the performance during
boot-up, as there are various clients using qrng during
bootup. Inorder to fix this problem, a daemon is introduced
which calls into kernel module (that sets low bandwidth).
This change supports the IOCTL call to disable the bus bandwidth.

Change-Id: I386d1eb4c50c057ae2852e7f9d47c8db8e522ca5
Signed-off-by: Hariprasad Dhalinarasimha <hnamgund@codeaurora.org>