mips32r2_common: timer fixes

[cladmi]

Contribution description

Fix return value for timer_ function that should return 1 on success.

mips32r2_common already implements timer_set so it should not be provided by
periph_common/timer to avoid multiple definition errors hidden by the linker.

The firmware was using the one from mips32r2_common before (binary checked).
So the final linked version is the same.

This PR is using a commit from #8711 with added info in the commit message.

Verification

I checked what was built with:

mips-mti-elf-objdump -d bin/mips-malta/mips32r2_common_periph/timer.o bin/mips-malta/periph_common/timer.o bin/
mips-malta/*.elf | grep -A 30 '<timer_set>:'

And the timer_set implementation is the same before and after the fix.

Issues/PRs references

It is required for #8711 and replaces #8720 which raised other problems.

[neiljay]

It looks good to me, I have not checked it on target hardware yet, that may take a few days.

But I cannot see why there would be any issues and you have checked the resultant binary is unchanged.

So if you want to merge this soon to resolve another issue please go ahead.

Is there a plan to fix the race in the generic implementation ?

[cladmi]

@neiljay I have not followed the generic implementation case for the moment, I did not exactly got the problem, so hard to do a PR if I miss some points.

[cladmi]

@neiljay do you think you will have time to test it for the release ?

[neiljay]

@cladmi Just tested on pic32-wfire with timer_periodic_wakeup and it looks good:

main(): This is RIOT! (Version: 2017.01-devel-1551-gbbd6a-ldt-n-jones-heads/cladmi/pr/ld/mips32r2_timer_set)
slept until 1002496
slept until 2002944
slept until 3002368
slept until 4002816
slept until 5002240
slept until 6002688
slept until 7002112
slept until 8002560
slept until 9003008
slept until 10002432
slept until 11002880
slept until 12002304
slept until 13002752
slept until 14002176
slept until 15002624
slept until 16002048
slept until 17002496
slept until 18002944
slept until 19002368
slept until 20002816
slept until 21002240
slept until 22002688
slept until 23002112
slept until 24002560
slept until 25003008
slept until 26002432
slept until 27002880

[cladmi]

Thanks