Fix split apk paths.

Soong has been outputting incorrect Android.mk entries for split apks.
soong_app_prebuilt.mk expects LOCAL_SOONG_BUILT_INSTALLED to contain a
list of <split apk path>:<on device install path> pairs whereas Soong
outputs <split apk path>:$(LOCAL_MODULE_PATH)/<split apk filename> pairs.

This also adds a missing underscore in split apk filenames.

Test: m Split
Bug: 140795853
Change-Id: I3d6506f5e12106174fbbaef34749a272b5e1b90c