[PATCH v3] score: Fix simple timecounter support

[Martin Galvan]

Thanks a lot for this patch. We've tested it and so far it's working fine.
However we have a couple of questions:

1) Is there a reason why you're using the ARMV7M_Timecounter struct instead of
simply having a global boolean like we did in our patch? That pointer casting
trick seems a bit unsafe.

2) I saw you're using rtems_interrupt_disable/enable instead of
Timecounter_Acquire/Release. Is there any particular reason for this?