Use RSA-SHA256 in place of ECDSA256

TPM1.2 does not support ECC; ECC support is mandatory starting in TPM2.0. To support older, TPM1.2
devices, switch to using RSA-SHA256 instead of ECDSA256.

Bug: b/242622525
Change-Id: Ia35548280c553e30f30d235a7ed1431af2132875
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3866603


Commit-Queue: Christine Franks <christyfranks@google.com>
Reviewed-by: Darren Krahn <dkrahn@chromium.org>
Reviewed-by: James Cook <jamescook@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1045333}