drm/i915/hdcp: replace BIT() with REG_BIT() in register definitions

Registers contents are supposed to be defined using REG_BIT() to ensure
they're u32 and the shift is within bounds.

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Arun R Murthy <arun.r.murthy@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/d28b9b9fef4f496bdaaad5503dd8e0027f167518.1659607033.git.jani.nikula@intel.com