Android patch: Add '--small' option to makeconv call during .ucm to .cnv conversion

This change was introduced in Android by the ICU421 and ICU4.6 upgrades:

https://android.googlesource.com/platform/external/icu/+/85bf2e2
https://android.googlesource.com/platform/external/icu/+/27f6547

In ICU 64 build system has changed, migrating from Makefile to
python script when performing various data transformations, so that patch now
patches BUILDRULES.py and adds '--small' option there.

Test: n/a
Change-Id: Ice47b06b7c38071d6b243dcf4c17308ffd68bacf
1 file changed