dummycon: fix default rows/cols

dummycon fails to build on ARM/footbridge when the VGA console is
disabled, since I got the dependencies slightly wrong in a previous
patch:

drivers/video/console/dummycon.c: In function 'dummycon_init':
drivers/video/console/dummycon.c:27:25: error: 'CONFIG_DUMMY_CONSOLE_COLUMNS' undeclared (first use in this function); did you mean 'CONFIG_DUMMY_CONSOLE'?
   27 | #define DUMMY_COLUMNS   CONFIG_DUMMY_CONSOLE_COLUMNS
drivers/video/console/dummycon.c:28:25: error: 'CONFIG_DUMMY_CONSOLE_ROWS' undeclared (first use in this function); did you mean 'CONFIG_DUMMY_CONSOLE'?
   28 | #define DUMMY_ROWS      CONFIG_DUMMY_CONSOLE_ROWS

This only showed up after many thousand randconfig builds on Arm, and
doesn't matter in practice, but should still be fixed. Address it by
using the default row/columns on footbridge after all in that corner
case.

Fixes: 4293b092 ("dummycon: limit Arm console size hack to footbridge")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202409151512.LML1slol-lkp@intel.com/


Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Helge Deller <deller@gmx.de>