MIPS: Fix builds for VR41xx platforms

Changing inclusion of Platform files, broke VR41xx platforms. Add Makefile
to vr41xx directory and traverse subdirs from it.

Fixes: 26bff9eb ("MIPS: Only include the platformfile needed")
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

arch/mips/vr41xx/Makefile

+# SPDX-License-Identifier: GPL-2.0
+#
+obj-$(CONFIG_MACH_VR41XX)	+= common/
+obj-$(CONFIG_CASIO_E55)		+= casio-e55/
+obj-$(CONFIG_IBM_WORKPAD)	+= ibm-workpad/

arch/mips/vr41xx/Platform

 #
 # NEC VR4100 series based machines
 #
-platform-$(CONFIG_MACH_VR41XX)	+= vr41xx/common/
 cflags-$(CONFIG_MACH_VR41XX)	+= -I$(srctree)/arch/mips/include/asm/mach-vr41xx
 
 #
 # CASIO CASSIPEIA E-55/65 (VR4111)
 #
-platform-$(CONFIG_CASIO_E55)	+= vr41xx/casio-e55/
 load-$(CONFIG_CASIO_E55)	+= 0xffffffff80004000
 
 #
 # IBM WorkPad z50 (VR4121)
 #
-platform-$(CONFIG_IBM_WORKPAD)	+= vr41xx/ibm-workpad/
 load-$(CONFIG_IBM_WORKPAD)	+= 0xffffffff80004000
 
 #