naomi: detect Naomi 2 for decrypted .bin/.dat roms

[JoeMatt]

A decrypted single-file rom isn't in the romset table, so it was always
loaded as Naomi with the Naomi BIOS. A Naomi 2 game then ran without
the Elan and with the wrong BIOS.

The cartridge header starts with the board name ("NAOMI" or
"Naomi2"), the same field the loader already checks with GetBootId().
Read it before setPlatform() so a Naomi 2 rom gets the Naomi 2 platform,
and load naomi2.zip for it.

Only the game load path reads the header. getGamePlatform() is also
called by the boxart scrapers with just a file name, so it is unchanged.

Testing, libretro core on macOS (Vulkan/MoltenVK) with naomi2.zip:

• All 19 Naomi 2 dumps I have (Beach Spikers, Club Kart, Initial D 1-3, King of Route 66, VF4 / Evolution / Final Tuned, Virtua Striker 3, Wild Riders) have "Naomi2" at offset 0. Virtual-On, a Naomi 1 game, has "NAOMI" and still loads as Naomi.
• Beach Spikers and Initial D now load as Naomi 2 with naomi2.zip and run 1800 frames without errors in most runs (I did not check the picture).
• Beach Spikers intermittently loses the Vulkan device on MoltenVK (GPU page fault). That isn't from this change: unmodified dev does the same with the MAME romset (beachspi.zip + gds-0014.chd), 1 run in 5. Initial D didn't hit it in 3 runs.

🤖 Generated with Claude Code

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