drivers: litex_timer: Fix IRQ lock intolerance

This reimplements z_timer_cycle_get_32() so it works
when IRQs are locked and solves the hung
k_busy_wait() problem.

Fixes #23622.

Signed-off-by: Jakub Cebulski <jcebulski@internships.antmicro.com>
Signed-off-by: Tomasz Gorochowik <tgorochowik@antmicro.com>
Signed-off-by: Mateusz Holenko <mholenko@antmicro.com>

Co-authored-by: Tomasz Gorochowik <tgorochowik@antmicro.com>