Add two config flags for each hart for a bootloader nuttx:
CONFIG_MPFS_HARTx_SBI :
- select whether the hart boots via opensbi or not.
CONFIG_MPFS_HARTx_ENTRYPOINT :
- the target address to jump to, either directly from startup code or
from SBI if CONFIG_MPFS_HARTx_SBI is set
This allows building a nuttx based bootloader application, which can load
different applications/OSs for individual harts and jump to those
Signed-off-by: Jukka Laitinen <jukkax@ssrc.tii.ae>