Clear SAMD TAMPER interrupt in pinalarm properly

[dhalbert]

• Fixes DisplayIO not drawing on screen in 7.1.0 Beta 2 #5705.

• In SAMD, alarm_pin_pinalarm_reset() was clearing the TAMPER interrupt flag with a bitwise operation, instead of just writing a 1 to the right bit, with the rest zeros, using a full register write. The bitwise operation apparently caused the other RTC interrupts to be messed up in some way, and then caused problems with other timing-based operations (probably background task handling), and showed up as displayio problems.

• Based on the error above, looked for and fixed a few other INTENCLR.bit and INTENSET.bit assignments that should ahve been full-width register writes instead, and found a few. Tested frequencyio to make sure it still works. Did not test watchdog; there is only 1 active bit in that register anyway.

• Unrelated improvement found when seeing if this was a gc-related bug (which it was not): keypad module dict was mutable, but it could be constant. This was probably a leftover of an earlier version of keypad.

[jepler]

thank you!

[deshipu]

I wonder if this also fixes #5476, I will test next weekend.

[tannewt]

Interesting find! SVD files have a way to designate registers as writeOneToClear or writeOneToSet. I wonder if I've added this issue elsewhere. It should be fine with set as long as no logic is triggered in the peripheral.