coccicheck: replace --very-quiet with --quiet when debugging

coccicheck: replace --very-quiet with --quiet when debugging

When debugging (using --profile or --show-trying) you want to
avoid supressing output,  use --quiet instead. While at it, extend
documentation for SPFLAGS use.

For instance one can use:

$ export COCCI=scripts/coccinelle/misc/irqf_oneshot.cocci
$ make coccicheck DEBUG_FILE="poo.err" MODE=report SPFLAGS="--profile --show-trying" M=./drivers/mfd/arizona-irq.c

Expand Documentation/coccinelle.txt as well.

v4: expand Documentation/coccinelle.txt
v3: rebased, resolve conflicts, expand Documentation/coccinelle.txt
v2: use egrep instead of the *"=--option"* check, this doesn't work for
    disjunctions.

Signed-off-by: Luis R. Rodriguez <mcgrof@kernel.org>
Acked-by: Julia Lawall <julia.lawall@lip6.fr>
Signed-off-by: Michal Marek <mmarek@suse.com>