configs: k2g_evm: make sure config fallbacks take effect

Since config fallbacks contained in include/config_fallbacks.h
come into k2g_evm.h file through ti_armv7_keystone2.h, it should
be the last file included.

Without this, #define of FAT_WRITE when environment is in FAT
does not happen as the environment location is decided later
in the file.

Similar issues can come with other config fallbacks implemented.

Signed-off-by: Sekhar Nori <nsekhar@ti.com>