arch/x86: remove weak car_stage_entry() symbol

Many (if not all) platforms have moved to using consistent
boot flow constructs where a weak car_stage_entry() is no longer
necessary to avoid the complexity of handling the numerous and
different boot flow combinations. The weak symbol is just causing
issues so remove it.

Change-Id: I7e7897c0609aac8eef96a08bb789374b2403956d
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/35135
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-by: Subrata Banik <subrata.banik@intel.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/arch/x86/assembly_entry.S

@@ -60,9 +60,7 @@ debug_spinloop:
 #endif
 	call	car_stage_entry
 
-/* This is here for linking purposes. */
-.weak car_stage_entry
-car_stage_entry:
+	/* Expect to never return. */
 1:
 	jmp	1b