Repeat kapt processor argument for multiple processors

kapt claims to support a comma separated list of annotation
processors, but it errors if multiple annotation processors
are given.  Surrounding the the list with {} does not error,
but it also doesn't even warn if the second element in the
list is garbage, so it may not be running the second
processor.  Repeat the processor argument for each
annotation processor class instead.

Bug: 154736649
Test: TestKapt
Test: m checkbuild
Change-Id: I4c7c161dbf867d7fba1aaf16fd5e502647e3f682