kernel: move linux, part-probe dt parsing in generic code

The "linux,part-probe" dts parsing is a pretty neat generic feature.
It has been posted to kernel.org and could easily be reused by all
targets.

This change moves the patch to the 3.18 and 4.1 generic folders, and
makes the feature available to all platforms who may want to use it.

Signed-off-by: Mathieu Olivari <mathieu@codeaurora.org>
Acked-by: Hauke Mehrtens <hauke@hauke-m.de>

SVN-Revision: 46654

target/linux/generic/patches-3.18/406-mtd-old-rootfs-squashfs-splitter.patch

@@ -14,7 +14,7 @@
  	default y
 --- a/drivers/mtd/mtdpart.c
 +++ b/drivers/mtd/mtdpart.c
-@@ -681,6 +681,47 @@ mtd_pad_erasesize(struct mtd_info *mtd,
+@@ -682,6 +682,47 @@ mtd_pad_erasesize(struct mtd_info *mtd,
  	return len;
  }
  
@@ -62,7 +62,7 @@
  #define UBOOT_MAGIC	0x27051956
  
  static void split_uimage(struct mtd_info *master, struct mtd_part *part)
-@@ -743,7 +784,10 @@ static void mtd_partition_split(struct m
+@@ -744,7 +785,10 @@ static void mtd_partition_split(struct m
  		return;
  
  	if (!strcmp(part->mtd.name, "rootfs")) {