drm/i915: Move the dg2 fixed_enable_delay power well param to a common bitfield

The DG2 fixed delay duration is always 600usec, so save some space in
the power well descriptors by converting the parameter to a flag. While
at it also use a bitfield for both the always_on and fixed_enable_delay
flag.

This change also lets simplifying the definiton of power wells sharing
the same flags in an upcoming patch.

Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Jouni Högander <jouni.hogander@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220414210657.1785773-4-imre.deak@intel.com