drm/i915: Make power domain masks 64 bit long

There are currently 30 power domains, which puts us pretty close to the
limit with 32 bit masks. Prepare for the future and increase the limit
to 64 bit.

v2: Rebase
v3: s/unsigned long long/u64/ (Joonas)
    Allow the 64th bit of the mask to be used. (Joonas)

Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Ander Conselvan de Oliveira <ander.conselvan.de.oliveira@intel.com>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170209093121.24410-1-ander.conselvan.de.oliveira@intel.com