build: add ACS_LEVEL CMake flag for baremetal compliance level

[chetan-rathore]

Introduce a CMake build-time option, -DACS_LEVEL=, that overrides the per-platform PLATFORM_OVERRIDE__LEVEL compliance level for baremetal ACS runs.

Accepted values:

• Positive integer : sets ctx->level_value = and selects LVL_FILTER_MAX (run all rules with level <= n). Per-ACS valid ranges are validated at configure time: bsa=1, sbsa=3..7, pc_bsa=1; out-of-range values produce a warning and are clamped at runtime.
• 'fr' (case-insensitive): selects LVL_FILTER_FR (future-requirements mode); ctx->level_value is left at the platform default.

When ACS_LEVEL is not set, the existing platform header default is used.

Changes:

• CMakeLists.txt: validate ACS_LEVEL, define ACS_LEVEL= or ACS_LEVEL_FR for the C sources, and forward the value to nested wrapper builds via DEFAULT_OVERRIDE_ARGS.
• apps/baremetal/{bsa,sbsa,pc_bsa}_main.c: honor ACS_LEVEL / ACS_LEVEL_FR when applying user config defaults; existing runtime range clamping is preserved.
• pal/baremetal/module_config.rst: document the new flag and accepted values.

Change-Id: I01221549662678a61b3ecf57439a79fb29c9b64d

[chetan-rathore]

The SBSA NIST failure is not due to PR changes, but due to recent changes in edk2-libc which resulting in patch apply failures.

SBSA NIST needs to be regenerated, will be taken in separate ticket.

edk2-libc change reference: tianocore/edk2-libc@e9fed83