efi/runtime-wrappers: Use type safe encapsulation of call arguments

The current code that marshalls the EFI runtime call arguments to hand
them off to a async helper does so in a type unsafe and slightly messy
manner - everything is cast to void* except for some integral types that
are passed by reference and dereferenced on the receiver end.

Let's clean this up a bit, and record the arguments of each runtime
service invocation exactly as they are issued, in a manner that permits
the compiler to check the types of the arguments at both ends.
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

include/linux/efi.h

@@ -1264,23 +1264,21 @@ enum efi_rts_ids {
 	EFI_QUERY_CAPSULE_CAPS,
 };
 
+union efi_rts_args;
+
 /*
  * efi_runtime_work:	Details of EFI Runtime Service work
- * @arg<1-5>:		EFI Runtime Service function arguments
+ * @args:		Pointer to union describing the arguments
  * @status:		Status of executing EFI Runtime Service
  * @efi_rts_id:		EFI Runtime Service function identifier
  * @efi_rts_comp:	Struct used for handling completions
  */
 struct efi_runtime_work {
-	void *arg1;
-	void *arg2;
-	void *arg3;
-	void *arg4;
-	void *arg5;
-	efi_status_t status;
-	struct work_struct work;
-	enum efi_rts_ids efi_rts_id;
-	struct completion efi_rts_comp;
+	union efi_rts_args	*args;
+	efi_status_t		status;
+	struct work_struct	work;
+	enum efi_rts_ids	efi_rts_id;
+	struct completion	efi_rts_comp;
 };
 
 extern struct efi_runtime_work efi_rts_work;