All timespec passed from/to user-space are now y2038-compliant
(i.e. tv_sec is 64bit wide), using the __evl_timespec and
__evl_itimerspec type definitions at kernel boundary. Conversions
happen back and forth between these types and the timespec64 and
itimerspec64 types used internally.

Invariant: __evl_timespec and __evl_itimerspec are compatible bitwise
with __kernel_timespec and __kernel_itimerspec respectively. libevl
does assume so.

Also:

- The sanitization fixes the ABI so that timespec and itimerspec
  structs are always passed by address, ensuring -EFAULT on invalid
  pointer received from the user, instead of putting the latter at
  risk of SIGSEGV by forcing it to copy/dereference these arguments.

- what EVL_CLKIOC_ADJ_TIME should do was never specified in the
  context of an EVL clock, and no defined use case ever
  existed. However, this service caused a y2038 problem due to the
  legacy timex struct argument. This service was removed from the ABI.

Signed-off-by: Philippe Gerum <rpm@xenomai.org>