ARM: keystone2: keystone_nav: make it dependent on keystone driver

This driver is needed in case if keystone driver is used.
Currently only keystone_net driver uses it. So to avoid
redundant code compilation make the keystone_nav dependent
on keystone net driver. It also leads to compilation errors
for boards that does't use it.

Acked-by: Murali Karicheri <m-karicheri2@ti.com>
Signed-off-by: Ivan Khoronzhuk <ivan.khoronzhuk@ti.com>

arch/arm/cpu/armv7/keystone/Makefile

@@ -10,7 +10,7 @@ obj-y	+= psc.o
 obj-y	+= clock.o
 obj-y	+= cmd_clock.o
 obj-y	+= cmd_mon.o
-obj-y	+= keystone_nav.o
+obj-$(CONFIG_DRIVER_TI_KEYSTONE_NET) += keystone_nav.o
 obj-y	+= msmc.o
 obj-$(CONFIG_SPL_BUILD)	+= spl.o
 obj-y	+= ddr3.o