x86/irq: Define trace events conditionally

When both of X86_LOCAL_APIC and X86_THERMAL_VECTOR are disabled,
the irq tracing produces a W=1 build warning for the tracing
definitions:

  In file included from include/trace/trace_events.h:27,
                 from include/trace/define_trace.h:113,
                 from arch/x86/include/asm/trace/irq_vectors.h:383,
                 from arch/x86/kernel/irq.c:29:
  include/trace/stages/init.h:2:23: error: 'str__irq_vectors__trace_system_name' defined but not used [-Werror=unused-const-variable=]

Make the tracepoints conditional on the same symbosl that guard
their usage.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20250225213236.3141752-1-arnd@kernel.org