kernel/linux: fix using custom location

Currently, extract and patch are skipped as thus:
- using a custom directory of pre-installed headers
- a correctly named directory already exists

Otherwise, extract and patch are done.

The current second condition is wrong, because it allows the following
sequence to happen:
- a non-custom kernel is used
- a previous build only partially extracted the non-custom sources
- that p[revious build broke during extraction (eg. incomplete tarball...)
- a subsequent build will find a properly named directory, and will
thus skip extract and patch, which is wrong

Fix that by following the conditions in this table:

Type | Extract | Patch
----------------------+---------+-------
Pre-installed headers | N | N
custom directory | N | N
custom tarball | Y | N
mainstream tarball | Y | Y

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: David Holsgrove <david.holsgrove@xilinx.com>

# Test suite config options

if EXPERIMENTAL

menu "Test suite"

config TEST_SUITE

    bool

config TEST_SUITE_GCC

    bool

    prompt "GCC test suite"

    depends on EXPERIMENTAL

    select TEST_SUITE

    help

      Select this option to install the GCC test suite in $CT_PREFIX_DIR/test_suite.

      The GCC test suite includes a collection of various toolchain tests for GCC -

      it utilizes the DejaGnu test framework.

      For some tests a network enabled target with ssh server is required.

      A helper Makefile is provided for running the tests - please see the included

      README for information on how to run the test suite.

endmenu

endif