drivers: lora: hal_common: Offload calling TimerIrqHandler to work queue

Since TimerIrqHandler() API does SPI transactions, it is not advised to
call from an IRQ context. Hence, offload it to a work queue.

Reported-by: Andreas Sandberg <andreas@sandberg.pp.se>
Signed-off-by: Manivannan Sadhasivam <mani@kernel.org>