drm/msm/hdmi: update HDMI_GEN_PKT_CTRL_GENERIC0_UPDATE definition

The GENERIC0_UPDATE field is a single bit. Redefine it as boolean to
simplify its usage in the driver.

Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/639660/
Link: https://lore.kernel.org/r/20250226-bridge-hdmi-connector-v8-5-340af24b35cc@linaro.org