ARM: omap: remove empty plat-omap directory

The last file in this directory is gone, and it can be removed as well.
Acked-by: NTony Lindgren <tony@atomide.com>
Signed-off-by: NArnd Bergmann <arnd@arndb.de>

arch/arm/Makefile

@@ -228,7 +228,6 @@ machine-$(CONFIG_PLAT_SPEAR)		+= spear
 
 # Platform directory name.  This list is sorted alphanumerically
 # by CONFIG_* macro name.
-plat-$(CONFIG_ARCH_OMAP)	+= omap
 plat-$(CONFIG_PLAT_ORION)	+= orion
 plat-$(CONFIG_PLAT_PXA)		+= pxa
 plat-$(CONFIG_PLAT_VERSATILE)	+= versatile

arch/arm/plat-omap/Makefile

-# SPDX-License-Identifier: GPL-2.0-only
-#
-# Makefile for the linux kernel.
-#
-
-ccflags-$(CONFIG_ARCH_MULTIPLATFORM) := -I$(srctree)/arch/arm/plat-omap/include
-
-# Common support
-obj-y :=