Clean up HalGroup::forEachInstance usage

Add a few functions to MatrixInstance to print
out human-readable strings so that analyze_matrix / vintf
can use them.

Bug: 140832836
Test: libvintf_test
Test: analyze_matrix --interfaces \
    --input hardware/interfaces/compatibility_matrices/compatibility_matrix.current.xml
Test: adb shell vintf

Change-Id: Ice13f299ba24808119f5536ecacc2777cfa870a2
8 files changed