arm: am437x: cm-t43: bring back BOOTDELAY feature

arm: am437x: cm-t43: bring back BOOTDELAY feature

Commit 755324 (configs: Use config_distro_defaults.h in ti_armv7_common.h)
made ti_armv7_common.h include config_distro_defaults.h. This breaks the
bootdelay feature in cm_t43 because now the
  - #include ti_armv7_common.h (#define CONFIG_BOOTDELAY 1)
  - #undef CONFIG_BOOTDELAY
  - #include config_distro_defaults.h (#define CONFIG_BOOTDELAY 2)
dance in cm_t43.h is no longer valid and in fact leads to CONFIG_BOOTDELAY
not being defined.

Adapt the config file to the new inclusion hierarchy.

Cc: Tom Rini <trini@konsulko.com>
Cc: Albert Aribaud <albert.u.boot@aribaud.net>
Cc: Igor Grinberg <grinberg@compulab.co.il>
Signed-off-by: Nikita Kiryanov <nikita@compulab.co.il>
Reviewed-by: Tom Rini <trini@konsulko.com>