Silabs spiflash bootloader: generic JEDEC fallback for unknown flash chips (#457)

The Gecko spiflash bootloader identifies the external SPI-NOR flash by its
JEDEC id (0x9F) against a hardcoded table. A chip not in the table makes
getDeviceType() return UNKNOWN_DEVICE, storage_init() then returns
BOOTLOADER_ERROR_INIT_STORAGE and the application never boots -- the module is
dead after flashing (#422). ZBMINIL2 ships with at least three different flash
chips, so this recurs per hardware variant and currently needs a per-chip
bootloader build.

Add a generic fallback: when the JEDEC id is not in the table but is plausible
(mfg byte not 0x00/0xFF, sane density code), serve it with a generic
standard-SPI-NOR profile whose size is derived from the JEDEC density code
(1 << code). The explicit table still matches first, so every already-supported
chip is byte-for-byte unchanged; only previously-unhandled chips are affected.
Gated by BTL_STORAGE_SPIFLASH_GENERIC_JEDEC (default on; set 0 to require an
explicit table match).

Tested on a real ZBMINIL2 whose Giantec GT25Q80A (JEDEC C4 60 14) is not in the
table: with this bootloader the module boots and rejoins the Zigbee network,
where before it was dead after flashing.

Refs #422

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>
Co-authored-by: Roman Skurikhin <romasku135@gmail.com>

Author: 3 people