Dockerfile: install libtspi
Dockerfile: install libtspi

This is needed to build go-attestation as TPM 1.2 support is currently
non-optional.

Signed-off-by: Joe Richey <24d3dd8348b5cac19a417e52b4f8141ba91506f0@google.com>

google/go-tpm-tools,google/go-tpm-tools,google/go-tpm-tools