ath79/mikrotik: load caldata via sysfs loader

ath79/mikrotik: load caldata via sysfs loader

This commit takes advantages of base-files 220 which introduces routines
to perform caldata loading directly via the kernel sysfs loader helper.
This has the benefits of not wasting flash space to store caldata.

Memory footprint is reduced to the bare minimum: for devices that don't
need MAC patching, the caldata is loaded directly, for devices that do
need MAC patching, the caldata is extracted to /tmp, patched and then
loaded.

Signed-off-by: Thibaut VARÈNE <hacks@slashdirt.org>