kernel: export ARCH and CROSS_COMPILE to all modules

Today it is not really important to do this because all our modules are
within the project itself. But, at somepoint, we may use submodules
in order to integrate drivers from external sources; so, we need to export
our default values because we will not have control over the other projects

Signed-off-by: Federico Vaga <federico.vaga@cern.ch>

kernel/Makefile

@@ -3,6 +3,8 @@ DIRS = wr_vic wr_nic wr_rtu at91_softpwm wr_pstats wr_clocksource
 
 # We may "LINUX ?= /usr/src/linux-wrswitch", but it's better to leave it empty
 
+export ARCH ?= arm
+export CROSS_COMPILE ?= $(CROSS_COMPILE_ARM)
 
 all modules clean:
 	for n in $(DIRS); do \