riscv: select CONFIG_PHYS_64BIT on RV64I systems

CONFIG_PHYS_64BIT should be enabled on RV64I systems. Select it.
Signed-off-by: NLukas Auer <lukas.auer@aisec.fraunhofer.de>
Reviewed-by: NBin Meng <bmeng.cn@gmail.com>
Reviewed-by: NRick Chen <rick@andestech.com>

arch/riscv/Kconfig

@@ -32,6 +32,7 @@ config ARCH_RV32I
 config ARCH_RV64I
 	bool "RV64I"
 	select 64BIT
+	select PHYS_64BIT
 	help
 	  Choose this option to target the RV64I base integer instruction set.