Add build_mixed_kernels_ramdisk to otatools.zip

Bug: 381198695
Test: lunch cf_x86_64_phone-trunk_staging-userdebug && m otatools-package dist, out/dist/otatools.zip should contain bin/build_mixed_kernels_ramdisk
Ignore-AOSP-First: submit with ag/30720005 and then cherrypick to AOSP
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:481aae6e078e089fd096446e28c41cf30e820951)
Merged-In: I1c12d04db924b0f1a47f38f3c253178c46dbef11
Change-Id: I1c12d04db924b0f1a47f38f3c253178c46dbef11