cubox-i: Use linux-fslc by default

linux-cubox-i has been broken for quite some time as it does not
contain the GCC5 fixes, for example.

Let's make 'linux-fslc' the default kernel and remove
the non-working 'linux-cubox-i' kernel.

Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>

conf/machine/cubox-i.conf

@@ -14,7 +14,7 @@ require conf/machine/include/tune-cortexa9.inc
 
 SOC_FAMILY = "mx6:mx6dl:mx6q"
 
-PREFERRED_PROVIDER_virtual/kernel = "linux-cubox-i"
+PREFERRED_PROVIDER_virtual/kernel ?= "linux-fslc"
 
 UBOOT_MAKE_TARGET = ""
 UBOOT_SUFFIX = "img"