travis: add some targets, we cache git clone stuff now on distfiles.openadk.org, timeout shouldn't be reached

.travis.yml

@@ -9,7 +9,11 @@ git:
   depth: 3
 matrix:
   include:
-  - env: ARCH=arm SYSTEM=linksys-nslu2
+  - env: ARCH=arm SYSTEM=linksys-nslu2 ENDIAN=big
+  - env: ARCH=arm SYSTEM=raspberry-pi
+  - env: ARCH=arm SYSTEM=raspberry-pi2
+  - env: ARCH=arm SYSTEM=raspberry-pi3
+  - env: ARCH=arm SYSTEM=beaglebone-black
   - env: ARCH=avr32 SYSTEM=atmel-ngw100
   - env: ARCH=avr32 SYSTEM=grasshopper
   - env: ARCH=cris SYSTEM=foxboard-lx832