Revert "hwrng: mpfs - Enable COMPILE_TEST"

This reverts commit 6a71277c.

The underlying option POLARFIRE_SOC_SYS_CTRL already supports
COMPILE_TEST so there is no need for this.  What's more, if
we force this option on without the underlying option it fails
to build.

Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>