Update keymaster API to final signing spec

Update keymaster API to final signing spec

Switch from unspecified encoding for import of keys to PKCS#8 (Java
standard encoding).

Add function for obtaining the public key from a keypair.

Add fields for RSA key generation that indicate modulus size and desired
public exponent.

Add in placeholder fields for possible digest and padding types for
signatures. Currently the only thing supported is "none" and "none"
respectively.

Change-Id: I19ee02cf35321aee859e2460a963c7213791414b