SX127X improvements
drivers/wireless/lpwan/sx127x/sx127x: add TX power configuration
drivers/wireless/lpwan/sx127x/sx127x: discard RX packets with unsupported length
drivers/wireless/lpwan/sx127x/sx127x: refactor some logic
drivers/wireless/lpwan/Kconfig: move some hardcoded sx127x configuration to Kconfig
drivers/wireless/lpwan/Kconfig: remove EXPERIMENTAL flag
configs/b-l072z-lrwan1/sx127x: board-specific sx127x configuration
configs/nucleo-f091rc/sx127x: board-specific sx127x configuration
configs/nucleo-l073rz/sx127x: board-specific sx127x configuration
LORA and FSK look fine but there is something missing for OOK and communication is not working yet.
Approved-by: Gregory Nutt <gnutt@nuttx.org>
