coresight: Fix missing include for FIELD_GET

coresight: Fix missing include for FIELD_GET

Include the header for FIELD_GET which is only sometimes transitively
included on some configs and kernel releases.

Reported-by: Linux Kernel Functional Testing <lkft@linaro.org>
Closes: https://lists.linaro.org/archives/list/lkft-triage@lists.linaro.org/thread/6GKMK52PPRJVEYMEUHJP6BXF4CJAXOFL/
Fixes: a4e65842e114 ("coresight: Only check bottom two claim bits")
Signed-off-by: James Clark <james.clark@linaro.org>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Link: https://lore.kernel.org/r/20250707-james-coresight-bitfield-include-v1-1-aa0f4220ecfd@linaro.org