Fix HDMI sink compatibility for Samsung TVs and strict monitors

[BrentRector]

Summary

Files: hdl/hdmi/hdmi.sv, hdl/hdmi/audio_clock_regeneration_packet.sv, hdl/hdmi/packet_picker.sv

Samsung TVs and some strict HDMI monitors (e.g. Ingnok portable displays) reject the A2FPGA
HDMI signal entirely, showing no video. The root cause is multiple HDMI spec violations in
the packet generation that lenient sinks tolerate but strict sinks reject.

Fixes

• AVI InfoFrame fields: Set PICTURE_ASPECT_RATIO to match VIC, ACTIVE_FORMAT_INFO_PRESENT=1,
  SCAN_INFO=underscan, RGB_QUANTIZATION_RANGE=full (0-255) — instead of relying on defaults
  that some sinks interpret as "undefined"
• Non-deterministic X values: Replace X values in null packet and ACR headers with zeros
  so BCH ECC checksums are consistent across synthesis runs
• Packet type reset: Fix packet_type reset to 8'd0 (null) instead of 8'dx for
  deterministic mux behavior between field_end and packet_enable
• Blocking assignment fix: Change control_data from blocking (=) to non-blocking (<=)
  assignment in HDMI mode reset path (sequential always_ff block)

How Discovered

Testing A2FPGA output on a Samsung TV produced no video at all. The TV's HDMI input simply
showed "No Signal." Investigation revealed the packet generation had missing InfoFrame fields
and non-deterministic packet content that strict sinks rejected.

Note: This is a companion to PR #35 which addresses HDMI control period timing from the
upstream hdl-util/hdmi library. This PR fixes additional compatibility issues in the A2FPGA-
specific packet generation code.

Test Plan

• Samsung TV displays A2FPGA video correctly (was "No Signal" before fix)
• Ingnok portable monitor displays correctly
• No regression on previously-working HDMI sinks (Dell monitor, LG TV)