Allow variable numbers of typemap in mojo generations

As example, device/google/cheets2/camera doesn't add additional
typemap and libarcbrigge needs to have multiple typemaps.

Bug: 27569341
Test: mmma -j32 external/libmojo (in AOSP branch), mmma -j32
device/google/cheets2/camera/mojo (in master), mmma -j32
vendor/google_arc/libs/libarcbridgeservice (in master).

Change-Id: Ifb5e045c7dd8ec658dce7cb688e7ffaa71b837bb
1 file changed