Add support to patch QCDT

Old Qualcomn devices have their own special QC table of DTB to
store device trees. Since patching fstab is now mandatory on Android 10,
and for older devices all early mount devices have to be included into
the fstab in DTBs, patching QCDT is crucial for rooting Android 10
on legacy devices.

Close #1876 (Thanks for getting me aware of this issue!)

native/jni/magiskboot/format.h

@@ -41,6 +41,7 @@ typedef enum {
 #define DTB_MAGIC       "\xd0\x0d\xfe\xed"
 #define LG_BUMP_MAGIC   "\x41\xa9\xe4\x67\x74\x4d\x1d\x1b\xa4\x29\xf2\xec\xea\x65\x52\x79"
 #define DHTB_MAGIC      "\x44\x48\x54\x42\x01\x00\x00\x00"
+#define QCDT_MAGIC      "QCDT"
 #define SEANDROID_MAGIC "SEANDROIDENFORCE"
 #define TEGRABLOB_MAGIC "-SIGNED-BY-SIGNBLOB-"
 #define NOOKHD_RL_MAGIC "Red Loader"