scripts/gen_image_generic.sh: allow passing in partition offset

Allow passing in an optional offset (PARTOFFSET) for the first partition.
If not specified this will default to 256K (512 blocks) as it has before.

For example if you want to start partition data at a 16M offset instead
of 256K, specify 'PARTOFFSET=16M'.

Signed-off-by: Tim Harvey <[email protected]>

scripts/gen_image_generic.sh

@@ -19,7 +19,7 @@ head=16
 sect=63
 
 # create partition table
-set $(ptgen -o "$OUTPUT" -h $head -s $sect ${GUID:+-g} -p "${KERNELSIZE}m" -p "${ROOTFSSIZE}m" ${ALIGN:+-l $ALIGN} ${SIGNATURE:+-S 0x$SIGNATURE} ${GUID:+-G $GUID})
+set $(ptgen -o "$OUTPUT" -h $head -s $sect ${GUID:+-g} -p "${KERNELSIZE}m${PARTOFFSET:+@$PARTOFFSET}" -p "${ROOTFSSIZE}m" ${ALIGN:+-l $ALIGN} ${SIGNATURE:+-S 0x$SIGNATURE} ${GUID:+-G $GUID})
 
 KERNELOFFSET="$(($1 / 512))"
 KERNELSIZE="$2"