hwrng: mpfs - Enable COMPILE_TEST

The dependency on HW_RANDOM is redundant so this patch removes it.
As this driver seems to cross-compile just fine we could also enable
COMPILE_TEST.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>