defconfig: k2x_hs: Remove DTB_RESELECT to fix DHCP issue

This fixes the inadvertent definition of CONFIG_DTB_RESELECT and
CONFIG_MULTI_DTB_FIT in the K2x HS defconfigs, that happened as part of
a resync of the defconfigs.

The inclusion of these config options causes ethernet to stop working on
K2x HS devices as they interfere with the installation of the secure
boot monitor.

This patch also removes the above configs for the K2 GP devices, as they
are not needed, and to keep the differences between the GP and HS
defconfigs to a minimum.

Signed-off-by: Madan Srinivas <madans@ti.com>
Signed-off-by: Andrew F. Davis <afd@ti.com>