ACPI: ARM64: add acpi_iort.h to MAINTAINERS

IORT(Input Output Remapping Table) represents the I/O topology of an
Arm-based system for use with the ACPI, so acpi_iort.h is for arm64
only.

This helps git-send-email to figure out the proper maintainers when
touching the file.

Signed-off-by: Hanjun Guo <guohanjun@huawei.com>
Acked-by: Sudeep Holla <sudeep.holla@arm.com>
Link: https://lore.kernel.org/r/20240808130946.1028376-1-guohanjun@huawei.com


Signed-off-by: Will Deacon <will@kernel.org>