scripts/tags.sh: choose which directories to exclude from being indexed

It's common for drivers that share same physical components to also
duplicate source code (or at least portions of it). A good example is
both drivers/gpu/drm/amdgpu/* and drivers/gpu/drm/radeon/* have a header
file called atombios.h.

While their contents aren't the same, a lot of their structs have
the exact same names which makes navigating through the code base a bit
messy as cscope will show up 'references' across drivers which aren't
exactly correct.

Add IGNORE_DIRS variable, which specifies which directories
to be ignored from indexing.

Example:
        make ARCH=x86 IGNORE_DIRS="drivers/gpu/drm/radeon tools" cscope

Signed-off-by: Paulo Miguel Almeida <paulo.miguel.almeida.rodenas@gmail.com>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>
Reviewed-by: Vipin Sharma <vipinsh@google.com>
Link: https://lore.kernel.org/r/Y5jf59VCL/HAt60q@mail.google.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>