cpu/saml21/pm: allow blocking IDLE mode

[jue89]

Contribution description

This PR allow to block the IDLE mode on the saml21 cpu.

Testing procedure

Programming tests/periph_pm to a saml21-based board:

make -C tests/periph_pm BOARD=samr30-xpro flash term
2022-10-31 22:24:23,596 # main(): This is RIOT! (Version: 2023.01-devel-216-g4b802-fix/saml21-pm-modes)
2022-10-31 22:24:23,601 # This application allows you to test the CPU power management.
2022-10-31 22:24:23,607 # The available power modes are 0 - 2. Lower-numbered power modes
2022-10-31 22:24:23,612 # save more power, but may require an event/interrupt to wake up
2022-10-31 22:24:23,615 # the CPU. Reset the CPU if needed.
2022-10-31 22:24:23,617 # mode 0 blockers: 1 
2022-10-31 22:24:23,619 # mode 1 blockers: 1 
2022-10-31 22:24:23,621 # mode 2 blockers: 0 
2022-10-31 22:24:23,623 # Lowest allowed mode: 2
2022-10-31 22:24:23,626 # using BTN0 as wake-up source
2022-10-31 22:24:23,628 # pm_set(): setting IDLE mode.
> pm block 2
2022-10-31 22:24:55,455 # pm block 2
2022-10-31 22:24:55,457 # Blocking power mode 2.
> pm show
2022-10-31 22:24:59,751 # pm show
2022-10-31 22:24:59,752 # mode 0 blockers: 1 
2022-10-31 22:24:59,754 # mode 1 blockers: 1 
2022-10-31 22:24:59,756 # mode 2 blockers: 1 
2022-10-31 22:24:59,758 # Lowest allowed mode: 3
> pm unblock 2
2022-10-31 22:25:17,447 # pm unblock 2
2022-10-31 22:25:17,450 # Unblocking power mode 2.
2022-10-31 22:25:17,453 # pm_set(): setting IDLE mode.
> pm unblock 1
2022-10-31 22:25:20,823 # pm unblock 1
2022-10-31 22:25:20,826 # Unblocking power mode 1.
2022-10-31 22:25:20,829 # pm_set(): setting STANDBY mode.

Issues/PRs references

#13475 yielded #17895, which already prepared the saml21 CPUs to take the IDLE pm into account.
#17883 implements the same logic for the samd5x cpu family.

[riot-ci]

Murdock results

✔️ PASSED

4b802ad sys/pm_layered: add debugging outputs

Success	Failures	Total	Runtime
2000	0	2000	06m:45s

Artifacts

• Documentation preview

This only reflects a subset of all builds from https://ci-prod.riot-os.org. Please refer to https://ci.riot-os.org for a complete build for now.

[jue89]

Wow, that was fast! Thank you :)