[EC] Unify scalar_mul_base point for ec_nistp curves

[dkostic]

Issues:

CryptoAlg-2544

Description of changes:

Added unified scalar multiplication of the base point for curves
implemented in ec_nistp. This is a refactor of the algorithm in
p384.c and p521.c that makes it generic. The implementation
in p384.c and p521.c is substituted with this new unified
implementation.

Call-outs:

Point out areas that need special attention or support during the review process. Discuss architecture or design changes.

Testing:

How is this change tested (unit tests, fuzz tests, etc.)? Are there any testing steps to be verified by the reviewer?

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license and the ISC license.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.88%. Comparing base (ab8953b) to head (7ce5951).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2003      +/-   ##
==========================================
- Coverage   78.89%   78.88%   -0.01%     
==========================================
  Files         595      595              
  Lines      102451   102432      -19     
  Branches    14527    14519       -8     
==========================================
- Hits        80827    80804      -23     
  Misses      20976    20976              
- Partials      648      652       +4     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

---

🚨 Try these New Features:

• Flaky Tests Detection - Detect and resolve failed and flaky tests