drivers: mark static API structures as const to save RAM

[Copilot]

API structures (function pointer tables) in driver code were unnecessarily consuming RAM. These structures are never modified at runtime and should be stored in ROM/Flash.

Changes

Converted 27 static API structures to static const across 24 driver files:

• Emulation drivers (mspi, espi, bc12, eeprom, sensors)
• Network drivers (ethernet, nsos, loopback, canbus)
• Modem drivers (hl7800, hl78xx, wncm14a2a, ublox-sara-r4, sim7080, quectel-bg9x)
• Peripheral drivers (spi, watchdog, dp, firmware/scmi)

Example change:

-static struct ethernet_api virtnet_api = {
+static const struct ethernet_api virtnet_api = {
    .iface_api.init = virtnet_if_init,
    .get_capabilities = virtnet_get_capabilities,
    .send = virtnet_send,
};

This aligns with existing patterns where similar API structures are already correctly marked const.

Original prompt

in driver code, look for all structs that should be static const to save ram

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