configs: k2*_evm: rename skernel binary names to generated file names

using http://git.ti.com/keystone-linux/boot-monitor/trees/master

 as
reference (tag K2_BM_15.07) the generated files do not have evm
extensions by default. So dont use -evm extension.

Reviewed-by: Murali Karicheri <m-karicheri2@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Signed-off-by: Nishanth Menon <nm@ti.com>