Replace reserved field with version in DTBO header

The version filed(currently 0) will be incremented when the
dt_table_header struct is updated.

Bug: 77706975
Test: ./mkdtboimg_testdata.sh
Test: ./mkdtimg_testdata.sh

Change-Id: I5c08720132d024437cce40c68cc2c6e937a064fd
Merged-In: I5c08720132d024437cce40c68cc2c6e937a064fd
(cherry picked from commit 2626d8b9)