hwrng: msm: Setup RNG quality

The hwrng device can only contribute to the entropy pool if its quality
is non-zero. The current quality is zero which can lead to long boot
time on headless systems (without enough source of entropy).
Set the entropy quality of msm-rng to 700 (/1024), as defined in the
downstream kernel:

https://android.googlesource.com/kernel/msm/+/android-7.1.0_r0.2/drivers/char/hw_random/msm-rng.c#159



Signed-off-by: Loic Poulain <loic.poulain@linaro.org>