MATTER-6816: Added support for BRD9084B in release_2.10-1.6.1

[Arghya Dutta (silabs-ArghyaD)]

Issue Link: MATTER-6816

Description of Problem/Feature: Added support for BRD9084B in matter_extension for release_2.10-1.6.1.

Description of Fix/Solution:

• Added brd9084b to full Wi‑Fi SoC builds in .github/silabs-builds-siwx.json (used by Dev Apps CI via platform-builder.yaml)
• Ran slc/script/generate_metadata_hwfilter.py
  -- Added brd9084b to boardCompatibility for all Matter Wi‑Fi SoC templates in matter_templates.xml
  -- Added brd9084b demo entries in matter_demos.xml
  -- Added brd9084b to release notes board list in matter_docs.xml
  -- Added brd9084b to board_compatibility_matrix.html
• Enabled WSTK LEDs and 917 SoC LCD for brd9084b in matter_leds.slcc and matter_default_lcd_config.slcc

Testing Done:

• Tested local builds and basic sanity for non sleepy app.
• Tested full CI build for all supported sample apps for brd9084b - https://github.com/SiliconLabsSoftware/matter_extension/actions/runs/32043108404