trusty: fuzz: Link to libtrusty dynamically

libtrusty can be depended on by multiple thing in a fuzzer's
dependencies tree. It's no longer convenient to link to statically.

Leave tests statically linked. Test infra doesn't seem to handle shared
test libs correctly.

Bug: 171750250
Test: trusty_test_fuzzer libtrusty_coverage_test
Change-Id: Ic7d003151e43fb5bab63354fd42ea9667332743f