board: tbs2910: move CONFIG_BOOTCOMMAND from header to defconfig

This doesn't affect the size of the image: with
arm-linux-gnueabi-gcc 9.2.0-1 from the Parabola GNU/Linux
distribution, the text, data, bss and total sizes remain
unchanged.

Signed-off-by: Denis 'GNUtoo' Carikli <GNUtoo@cyberdimension.org>
Reviewed-by: Soeren Moch <smoch@web.de>
2 files changed