boot: nuttx: main: add suport for board late

initialization.

When using nuttx MCUBoot app as a main entry point in
place of nsh_main it is necesary to perform board-specific
driver initialization through boardctl().

Signed-off-by: Andrés Sánchez Pascual <tito97_sp@hotmail.com>

boot: nuttx: main: fix minor errors according

Signed-off-by: Andrés Sánchez Pascual <tito97_sp@hotmail.com>