HEVC ENC need to setting VA_RC_MB

[mypopydev]

User has to set VA_RC_MB when using VA_RC_CBR or VA_RC_VBR in HEVC ENC, but AVC encoding does not need to setting VA_RC_MB for CBR/VBR mode.

[XinfengZhang]

MBBRC should come from mb_rate_control, and driver should only set VA_RC_CBR or VBR ---- in the structure VAEncMiscParameterTypeRateControl. so driver only need to check VA_RC_CBR | m_encodeCtx->uiRCMethod