bpf: Enforce preallocation for instrumentation programs on RT

bpf: Enforce preallocation for instrumentation programs on RT

Aside of the general unsafety of run-time map allocation for
instrumentation type programs RT enabled kernels have another constraint:

The instrumentation programs are invoked with preemption disabled, but the
memory allocator spinlocks cannot be acquired in atomic context because
they are converted to 'sleeping' spinlocks on RT.

Therefore enforce map preallocation for these programs types when RT is
enabled.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200224145642.648784007@linutronix.de