arm: rmobile: Remove config.mk

Renesas ARM SoCs (R-Mobile, R-Car) are armv7 only.
This drops armv5 supprt from PLATFORM_CPPFLAGS and remove config.mk of
rmobile.

Signed-off-by: Nobuhiro Iwamatsu <nobuhiro.iwamatsu.yj@renesas.com>

arch/arm/cpu/armv7/rmobile/config.mk

@@ -1,9 +0,0 @@
-#
-# (C) Copyright 2002
-# Gary Jennejohn, DENX Software Engineering, <garyj@denx.de>
-#
-# SPDX-License-Identifier:	GPL-2.0+
-#
-
-# Make ARMv5 to allow more compilers to work, even though its v7a.
-PLATFORM_CPPFLAGS += -march=armv5