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

arch/riscv/Kconfig.erratas

@@ -46,7 +46,7 @@ config ERRATA_THEAD
 
 config ERRATA_THEAD_PBMT
 	bool "Apply T-Head memory type errata"
-	depends on ERRATA_THEAD && 64BIT
+	depends on ERRATA_THEAD && 64BIT && MMU
 	select RISCV_ALTERNATIVE_EARLY
 	default y
 	help
@@ -57,7 +57,7 @@ config ERRATA_THEAD_PBMT
 
 config ERRATA_THEAD_CMO
 	bool "Apply T-Head cache management errata"
-	depends on ERRATA_THEAD
+	depends on ERRATA_THEAD && MMU
 	select RISCV_DMA_NONCOHERENT
 	default y
 	help