riscv: make t-head erratas depend on MMU

Both basic extensions of SVPBMT and ZICBOM depend on CONFIG_MMU.
Make the T-Head errata implementations of the similar functionality
also depend on it to prevent build errors.

Fixes: a35707c3 ("riscv: add memory-type errata for T-Head")
Fixes: d20ec752 ("riscv: implement cache-management errata for T-Head SoCs")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Reviewed-by: Guo Ren <guoren@kernel.org>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20220907154932.2858518-1-heiko@sntech.de


Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>