ANDROID: vendor_hooks: Move TRACE_INCLUDE_PATH outside of hook headers

Right now, each vendor hook header file contains an unconditional
definition of TRACE_INCLUDE_PATH. This can however cause conflicts when
imported in subsystems that declare their own tracepoints without defining
TRACE_INCLUDE_PATH, expecting define_trace.h to use the default
<trace/events{system}.h> clause.

In the cgroup case, this forces us to #undef TRACE_INCLUDE_PATH before
importing the cgroup subsystem trace events header. However, one can notice
that TRACE_INCLUDE_PATH is only used by trace/define_trace.h, which itself
won't do anything if DECLARE_TRACE isn't defined. IOW, it isn't required
when one only requires forward declarations.

Prevent further headaches by containing the vendor hooks TRACE_INCLUDE_PATH
definition to vendor_hooks.c, where CREATE_TRACE_POINTS is also defined.

Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>