riscv: check for kernel config option in t-head memory types errata

The t-head variant of page-based memory types should also check first
for the enabled kernel config option.

Fixes: a35707c3 ("riscv: add memory-type errata for T-Head")
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: Guo Ren <guoren@kernel.org>
Link: https://lore.kernel.org/r/20220905111027.2463297-6-heiko@sntech.deSigned-off-by: Palmer Dabbelt <palmer@rivosinc.com>

arch/riscv/errata/thead/errata.c

@@ -17,6 +17,9 @@
 static bool errata_probe_pbmt(unsigned int stage,
 			      unsigned long arch_id, unsigned long impid)
 {
+	if (!IS_ENABLED(CONFIG_ERRATA_THEAD_PBMT))
+		return false;
+
 	if (arch_id != 0 || impid != 0)
 		return false;