init: create symlinks to block device nodes

eMMC block device names may change based on the detection order of
the eMMC device and any other SD bus devices, such as a removable SD
card.

This patch adds support to init for:
  * Symlinks to block devices.  When a block device uevent is
    processed, if it starts with "/devices/platform", the platform
    driver name is parsed out, and symlinks to the block device are
    created in /dev/block/platform/<platform driver>/
  * Symlinks based on partition name and number.  If the uevent for
    a block device contains information on the partition name or
    number, symlinks are created under
    /dev/block/platform/<platform driver>/by-num/p<partition>
    and
    /dev/block/platform/<platform driver>/by-name/<partition name>

init.rc can then use a device path like the following to mount an
eMMC device:
/dev/block/platform/<platform>/by-name/system /system ro

Change-Id: Id11bb7cdf1e2ada7752a5bd671cbf87237b34ae2
diff --git a/init/util.h b/init/util.h
index 4f473ec..3dadfb9 100644
--- a/init/util.h
+++ b/init/util.h
@@ -24,4 +24,8 @@
 time_t gettime(void);
 unsigned int decode_uid(const char *s);
 
+int mkdir_recursive(const char *pathname, mode_t mode);
+void sanitize(char *p);
+void make_link(const char *oldpath, const char *newpath);
+void remove_link(const char *oldpath, const char *newpath);
 #endif