Doc: misc-devices: move lcd-panel-cgram.txt to auxdisplay/

Commit 7005b584 ("Staging: add lcd-panel
driver") introduced the panel driver, which is now in
drivers/auxdisplay.

Cc: Willy Tarreau <w@1wt.eu>
Cc: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>