Specify KeyMint EC keys by curve not size

Future addition of extra curves means that key size is not enough to
identify the particular EC curve required. Use the EcCurve enum instead.

Bug: 226270116
Test: VtsHalRemotelyProvisionedComponentTargetTest
Change-Id: Ia6b7d86a387cfc06db05e4ba6ff8f331e9c6345f
Merged-In: Ia6b7d86a387cfc06db05e4ba6ff8f331e9c6345f
(cherry picked from commit 915ce253)