tty/vt: consolemap: rename and document struct uni_pagedir

tty/vt: consolemap: rename and document struct uni_pagedir

[ Upstream commit 4173f018aae16b6496d292c234b858241f85254f ]

struct uni_pagedir contains 32 unicode page directories, so the name of
the structure is a bit misleading. Rename the structure to uni_pagedict,
so it looks like this:
struct uni_pagedict
  -> 32 page dirs
     -> 32 rows
       -> 64 glyphs

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Link: https://lore.kernel.org/r/20220607104946.18710-2-jslaby@suse.cz
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Stable-dep-of: 03bcbbb3995b ("dummycon: Trigger redraw when switching consoles with deferred takeover")
Signed-off-by: Sasha Levin <sashal@kernel.org>