Driver-only ECC: auto-enable ECP_LIGHT when needed

[mpg]

This is split from #7390 - the original plan was for ECP_LIGHT to be auto-enabled when needed, but we then decided to first implement it as an internal symbol with no official way for users to enable (other that -D in CFLAGS), and address auto-enablement as a 2nd step.

We should auto-enable ECP_LIGHT in the following circumstances:

• When ECP_C is defined (done).
• When PK_C && USE_PSA && PSA_WANT_ALG_ECDSA, see Define (private) "light" subset of ECP #7410 (comment)
  • This will no more be needed after driver-only ECC: ECPf.PK testing #7453
• When MBEDTLS_PK_PARSE_EC_EXTENDED is defined.
• When support for parsing compressed points is requested, via a new option MBEDTLS_PK_PARSE_EC_COMPRESSED to be added as part of this task.
• When PSA_WANT_KEY_TYPE_ECC_KEY_PAIR_DERIVE is requested.

When this is done, the following changes can be made in all.sh:

• in component_test_psa_crypto_config_accel_all_ec_algs_use_psa() removed -DMBEDTLS_ECP_LIGHT as it's no longer needed (will be auto-enabled).
• in config_psa_crypto_full_all_ec_algs_no_ecp_use_psa() we need to disable any option that would re-enable ECP_LIGHT.

Depends on:

• Define PSA_WANT_KEY_TYPE_xxx_KEY_PAIR_yyy (step 1) #7614
• driver-only ECC: ECPf.PK testing #7453

[mpg]

Note: in the future we'll try to reduce the number of circumstances where ECP_LIGHT is auto-enabled.

• When PK_C && USE_PSA && PSA_WANT_ALG_ECDSA

This will be addressed by the next EPIC shortly, so that's quite temporary.

• When MBEDTLS_PK_PARSE_EC_EXTENDED is defined.

I think we could avoid that by having a table for how each curve we know is encoded as SpecifiedECDomain - I need to check though. If so, I'll create an issue in this EPIC to address that. Or perhaps we'll remove that in 4.0, and ignore it in the meantime.

• When support for parsing compressed points is requested - MBEDTLS_PK_PARSE_EC_COMPRESSED

This will have to wait for PSA to support compressed points somehow.

• When PSA_WANT_KEY_TYPE_ECC_KEY_PAIR_DERIVE is requested.

This will have to wait for the driver interface to support key derivation properly, see the dedicated EPIC.

[mpg]

Or perhaps we'll remove that in 4.0, and ignore it in the meantime.

See #6792 (comment)