riscv: select CONFIG_PHYS_64BIT on RV64I systems

CONFIG_PHYS_64BIT should be enabled on RV64I systems. Select it.

Signed-off-by: Lukas Auer <lukas.auer@aisec.fraunhofer.de>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Rick Chen <rick@andestech.com>
diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 7c76b4d..b81e0d9 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -32,6 +32,7 @@
 config ARCH_RV64I
 	bool "RV64I"
 	select 64BIT
+	select PHYS_64BIT
 	help
 	  Choose this option to target the RV64I base integer instruction set.