Kernel selftests: tpm2: check for tpm support

tpm2 tests set fails if there is no /dev/tpm0 and /dev/tpmrm0
supported. Check if these files exist before run and mark test as
skipped in case of absence.

Signed-off-by: Nikita Sobolev <Nikita.Sobolev@synopsys.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>