scripts/spdxcheck: Better statistics and exclude handling

spdxcheck -v output is just providing basic statistics, but lacks per
directory statistics.

Finding files without SPDX identifiers is cumbersome with spdxcheck, though
it has all the information required.

The exclude of files and directories is hardcoded in the script which makes
it hard to maintain and the information cannot be accessed by external tools.

The following series addresses this by adding:

 1) Directory statistics

    Incomplete directories: SPDX in Files
    ./                               :     6 of    13   46%
    ./Documentation                  :  4096 of  8451   48%
    ./arch                           : 13476 of 16402   82%
    ./block                          :   100 of   101   99%
    ./certs                          :    11 of    14   78%
    ./crypto                         :   145 of   176   82%
    ./drivers                        : 24682 of 30745   80%

 2) The ability to show files without SPDX

    Files without SPDX:
    ./kernel/cpu.c
    ./kernel/kmod.c
    ./kernel/relay.c

 3) A file based handling for exclude patterns

Thanks,

	tglx