Fix kconfig dependency warning:

WARNING: unmet direct dependencies detected for RISCV_ALTERNATIVE
  Depends on [n]: !XIP_KERNEL [=y]
  Selected by [y]:
  - ERRATA_THEAD [=y]

Fixes: a35707c3d850 ("riscv: add memory-type errata for T-Head")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Heiko Stuebner <heiko@sntech.de>
Cc: Paul Walmsley <paul.walmsley@sifive.com>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Palmer Dabbelt <palmer@rivosinc.com>
Cc: Albert Ou <aou@eecs.berkeley.edu>
Cc: linux-riscv@lists.infradead.org
---
 arch/riscv/Kconfig.erratas |    1 +
 1 file changed, 1 insertion(+)

--- a/arch/riscv/Kconfig.erratas
+++ b/arch/riscv/Kconfig.erratas
@@ -35,6 +35,7 @@ config ERRATA_SIFIVE_CIP_1200
 
 config ERRATA_THEAD
 	bool "T-HEAD errata"
+	depends on !XIP_KERNEL
 	select RISCV_ALTERNATIVE
 	help
 	  All T-HEAD errata Kconfig depend on this Kconfig. Disabling