native/mtd: implement .write_page()

[benpicco]

Contribution description

native didn't implement the new pagewise API yet, so unaligned writes / writes across page boundaries will fail.

Testing procedure

Issues/PRs references

#15362 (comment)

[jue89]

Does it really make sense to implement .write and .write_page separately?

The mtd driver would translate between both worlds if I understand its implementation correctly. So to me this is more or less redundant code - we don't loose functionality if we'd get rid of .write.

[jue89]

But all in all this PR fixes #15362 (comment) :)

git checkout benpicco/tests/mtd_raw
git checkout -b mtd_raw_test
git merge benpicco/native/mtd_pagewise
make -C tests/mtd_raw BOARD=native all term
(...)
/home/jue/Projects/RIOT/tests/mtd_raw/bin/native/tests_mtd_raw.elf  
RIOT native interrupts/signals initialized.
LED_RED_OFF
LED_GREEN_ON
RIOT native board initialized.
RIOT native hardware initialization complete.

main(): This is RIOT! (Version: 2021.01-devel-547-g4caa95-mtd_raw_test)
Manual MTD test
init MTD_0… OK (8192 kiB)
> test 0
test 0
[START]
[SUCCESS]

[benpicco]

Heh, looks like the unit test expects mtd_write() to fail on unaligned writes.
I'll move the 2nd commit to the other PR.

[bergzand]

Ack! Tested with tests/pkg_littlefs