msm: vidc: Allow all-intra encoding in CBR_CFR

CBR_CFR is one of the advertised rc mode for HEVC encoding.
However, all-intra is intended for quality bitstream. Hence,
fallback to VBR RC mode if client needs all-intra encoding.

Change-Id: Ib7cf49561f23076d136c58e0385db411e65883be
Signed-off-by: Amit Shekhar <ashekhar@codeaurora.org>