vt: redefine world of cursor macros

The cursor code used to use magic constants, ANDs, ORs, and some macros.
Redefine all this to make some sense.

In particular:
* Drop CUR_DEFAULT, which is CUR_UNDERLINE. CUR_DEFAULT was used only
  for cur_default variable initialization, so use CUR_UNDERLINE there to
  make obvious what's the default.
* Drop CUR_HWMASK. Instead, define CUR_SIZE() which explains it more.
  And use it all over the places.
* Define few more masks and bits which will be used in next patches
  instead of magic constants.
* Define CUR_MAKE to build up cursor value.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Cc: dri-devel@lists.freedesktop.org
Cc: linux-fbdev@vger.kernel.org
Link: https://lore.kernel.org/r/20200615074910.19267-25-jslaby@suse.cz


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>