We already had coverage for our new EVP_PKEY parsers, but it's good to have
some that cover them directly. The initial corpus was generated manually with
der-ascii and should cover most of the insanity around EC key serialization.

BUG=15

Change-Id: I7aaf56876680bfd5a89f5e365c5052eee03ba862
Reviewed-on: https://boringssl-review.googlesource.com/7728
Reviewed-by: Adam Langley <agl@google.com>