dumpsys: add option to list hardware services.

This gives a convenient way to dump information about hidl services.
When hidl services dump information themselves as well, that dump will
be made here as well.

Bug: 33382892
Test: dumpsys_test, dumpsys --hw works as expected
Change-Id: Ib08b5d052e63ed6260035ee8d3ad3dac296202b1