drivers: stepper: adi_tmc: diag0 interrupt support for tmc51xx

Add support for using the diag0 pin as an interrupt source. This
allows event detection via diag0 interrupts instead of polling rampstat.
The driver now:
- Configures diag0 when the GPIO is available
- Sets up GPIO interrupt handling for rising edge transitions for
rampstat reading
- Falls back to polling only when diag0 is not available

Signed-off-by: Dipak Shetty <shetty.dipak@gmx.com>