kconfig/lxdialog: Add definitions for mininimum (re)size values

Commit c8dc68ad0fbd ("kconfig/lxdialog: support resize") added support
for resizing, but forgot to collect all hardcoded values at one single
place.

Also add a definition for the check for a minimum screen/window size
of 80x19.

[ ChangeLog v3:
  * Rename MENU_{HEIGTH,WIDTH}_MIN -> MENUBOX_{HEIGTH,WIDTH}_MIN
  ChangeLog v2:
  * Rename WIN_{HEIGTH,WIDTH}_MIN -> WINDOW_{HEIGTH,WIDTH}_MIN
  * Mention the check for a minimum screen/window size in the changelog
  * Add a comment above the block of new definitions ]

Signed-off-by: Sedat Dilek <sedat.dilek@gmail.com>
Acked-by: Wang YanQing <udknight@gmail.com>
Tested-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
diff --git a/scripts/kconfig/lxdialog/textbox.c b/scripts/kconfig/lxdialog/textbox.c
index a48bb93..907cdcb 100644
--- a/scripts/kconfig/lxdialog/textbox.c
+++ b/scripts/kconfig/lxdialog/textbox.c
@@ -80,7 +80,7 @@
 
 do_resize:
 	getmaxyx(stdscr, height, width);
-	if (height < 8 || width < 8)
+	if (height < TEXTBOX_HEIGTH_MIN || width < TEXTBOX_WIDTH_MIN)
 		return -ERRDISPLAYTOOSMALL;
 	if (initial_height != 0)
 		height = initial_height;