cmake: make pde_C an optional top-level type.

RISCV has its own model of page tables that doesn't have a distinguished
'directory' level.

config.cmake

@@ -31,8 +31,7 @@ mark_as_advanced(${force} CSPEC_DIR SKIP_MODIFIES SORRY_BITFIELD_PROOFS UMM_TYPE
 add_custom_target(kernel_config_target)
 # Put our common top level types in
 set_property(TARGET kernel_config_target APPEND PROPERTY TOPLEVELTYPES
-    cte_C tcb_C endpoint_C notification_C asid_pool_C pte_C pde_C user_data_C
-    user_data_device_C
+    cte_C tcb_C endpoint_C notification_C asid_pool_C pte_C user_data_C user_data_device_C
 )
 
 ########################

src/arch/arm/config.cmake

@@ -43,6 +43,9 @@ config_choice(KernelARMPlatform ARM_PLAT "Select the platform for the architectu
 
 if(KernelArchARM)
     config_set(KernelSel4Arch SEL4_ARCH "${KernelArmSel4Arch}")
+    set_property(TARGET kernel_config_target APPEND PROPERTY TOPLEVELTYPES
+        pde_C
+    )
 endif()
 
 # arm-hyp masquerades as an aarch32 build

src/arch/x86/config.cmake

@@ -31,6 +31,9 @@ if(KernelArchX86)
     config_set(KernelSel4Arch SEL4_ARCH "${KernelX86Sel4Arch}")
     # x86 always has an FPU
     set(KernelHaveFPU ON)
+    set_property(TARGET kernel_config_target APPEND PROPERTY TOPLEVELTYPES
+        pde_C
+    )
 else()
     config_set(KernelPlatPC99 PLAT_PC99 OFF)
 endif()