base-files: add minimal mmc support

Added minimal mmc support for helper functions:

 - find_mmc_part: Look for a given partition name. Returns the
	coresponding partition path
 - caldata_extract_mmc: Look for a given partition name and then
	extracts the calibration data
 - mmc_get_mac_binary: Returns the mac address from a given partition
	name and offset

Signed-off-by: Davide Fioravanti <pantanastyle@gmail.com>
Signed-off-by: Robert Marko <robimarko@gmail.com>
[replace dd with caldata_dd, moved sysupgrade mmc to orbi]
Signed-off-by: Christian Lamparter <chunkeey@gmail.com>

package/base-files/files/lib/functions/system.sh

@@ -135,6 +135,15 @@ mtd_get_part_size() {
 	done < /proc/mtd
 }
 
+mmc_get_mac_binary() {
+	local part_name="$1"
+	local offset="$2"
+	local part
+
+	part=$(find_mmc_part "$part_name")
+	get_mac_binary "$part" "$offset"
+}
+
 macaddr_add() {
 	local mac=$1
 	local val=$2