support: add check_mem_access function

support: add check_mem_access function

Add check_mem_access(addr) function to check if memory at addr can
be written or read returning false if memory is not accessible.

This function changes signal handler for SIGSEGV and SIGBUS signals
when it is called first, and it is not thread-safe.

Co-authored-by: Adhemerval Zanella Netto <adhemerval.zanella@linaro.org>
Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>