selftests: sparc64: Fix to do nothing on non-sparc64

sparc64 test fails with the following errors on non-sparc64 systems. Fix
the Makefile to do nothing on non-sparc64 systems to suppress the errors:

make run_tests
adi-test.c: Assembler messages:
adi-test.c:302: Error: no such instruction: `rd %tick,%r13'
adi-test.c:304: Error: no such instruction: `rd %tick,%rbp'
adi-test.c:190: Error: no such instruction: `rd %tick,%rbp'
adi-test.c:192: Error: no such instruction: `rd %tick,%rdx'
adi-test.c:273: Error: no such instruction: `rd %tick,%rbx'
adi-test.c:276: Error: no such instruction: `rd %tick,%rdx'
adi-test.c:217: Error: no such instruction: `rd %tick,%rbp'
adi-test.c:220: Error: no such instruction: `rd %tick,%rdx'
adi-test.c:79: Error: no such instruction: `rd %tick,%rax'
adi-test.c:79: Error: no such instruction: `rd %tick,%rax'
adi-test.c:79: Error: no such instruction: `rd %tick,%rax'
adi-test.c:79: Error: no such instruction: `rd %tick,%rax'
adi-test.c:246: Error: no such instruction: `rd %tick,%rbp'
adi-test.c:248: Error: no such instruction: `rd %tick,%rdx'
adi-test.c:79: Error: no such instruction: `rd %tick,%rax'
adi-test.c:79: Error: no such instruction: `rd %tick,%rax'
adi-test.c:79: Error: no such instruction: `rd %tick,%rax'
<builtin>: recipe for target 'adi-test' failed
make[1]: *** [adi-test] Error 1
adi: [FAIL]
./drivers_test.sh: 24: ./drivers_test.sh: ./adi-test: not found
../lib.mk:73: recipe for target 'run_tests' failed
make: *** [run_tests] Error 1

Signed-off-by: Shuah Khan (Samsung OSG) <shuah@kernel.org>
Reviewed-by: Tom Hromatka <tom.hromatka@oracle.com>
Acked-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Shuah Khan (Samsung OSG) <shuah@kernel.org>