[Nexthop] Enable kernel config for interrupt-driven Xilinx I2C support

[siddarth-nexthop]

Pre-submission checklist

• I've ran the linters locally and fixed lint errors related to the files I modified in this PR. You can install the linters by running pip install -r requirements-dev.txt && pre-commit install
• pre-commit run

Summary

Enable the kernel config needed for interrupt-driven FPGA I2C support, replacing a polling-based AXI-IIC path with the upstream interrupt-driven xiic-i2c driver.

• CONFIG_I2C_XILINX=m: enables the upstream Xilinx AXI IIC platform driver (xiic-i2c) used for the FPGA I2C controllers.
• CONFIG_GPIO_PCI_IDIO_16=m: pulls in REGMAP_IRQ transitively, which is used by the parent PCI driver to demultiplex MSI vectors into per-controller Linux IRQs.

Test Plan

• Built an image with this config change.

• Verified on test hardware that the running kernel has the expected config and exports the required REGMAP_IRQ symbols.

Kernel config check:

grep -E "CONFIG_REGMAP_IRQ|CONFIG_I2C_XILINX|CONFIG_GPIO_PCI_IDIO_16" \
   /usr/src/kernels/$(uname -r)/.config /boot/config-$(uname -r) 2>/dev/null

Output:

CONFIG_REGMAP_IRQ=y
CONFIG_I2C_XILINX=m
CONFIG_GPIO_PCI_IDIO_16=m

Exported symbols check:

grep -E "regmap_irq_get_virq|devm_regmap_add_irq_chip" \
   /usr/src/kernels/$(uname -r)/Module.symvers || echo "REGMAP_IRQ symbols NOT exported by this kernel"

Output:

0x79b55a2a      devm_regmap_add_irq_chip_fwnode vmlinux EXPORT_SYMBOL_GPL
0xe27c38b7      devm_regmap_add_irq_chip        vmlinux EXPORT_SYMBOL_GPL
0x55784228      regmap_irq_get_virq             vmlinux EXPORT_SYMBOL_GPL

Hardware-tested with the built image. The system imaged successfully, booted into FBOSS, and platform bring-up completed successfully.