Specify bootconfig property in vendor_boot.img

bootconfig is a path to the text file, created based on
`INTERNAL_BOOTCONFIG` and `INTERNAL_BOOTCONFIG_FILE`. This is done by
auto generating a newly introduced bootconfig module. The
output file of the genrule module is passed as a property to the
vendor_boot.img module.

Test: Inspect the content of the generated vendor-bootconfig.img file
Test: Inspect the ninja command of the autogen vendor_boot.img
Bug: 379945468
Change-Id: I9c693de681e6dad7399f80df05825cce9b0c1c22