Add dummy vndk library libmkbootimg to enable abi checks on boot_img_hdr.

Bug: 74763691

Test: m -j libmkbootimg creates libmkbootimg.so.lsdump.

Test: make -j64

Change-Id: I8d716c560467aaf090f4f7ee9cfbc53a9405f05d
(cherry picked from commit 4cc755dc)