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>

# Template file for a debug utility

# Put your download code here

do_debug_foobar_get() {

    # For example:

    # CT_GetFile "foobar-${CT_FOOBAR_VERSION}" http://foobar.com/releases/

    :

}

# Put your extract code here

do_debug_foobar_extract() {

    # For example:

    # CT_Extract "foobar-${CT_FOOBAR_VERSION}"

    # CT_Patch "foobar" "${CT_FOOBAR_VERSION}"

    :

}

# Put your build code here

do_debug_foobar_build() {

    # For example:

    # mkdir -p "${CT_BUILD_DIR}/build-foobar"

    # CT_Pushd "${CT_BUILD_DIR}/build-foobar"

    # CT_DoExecLog CFG                                        \

    # "${CT_SRC_DIR}/foobar-${CT_FOOBAR_VERSION}/configure"   \

    #     --build=${CT_BUILD}                                 \

    #     --host=${CT_TARGET}                                 \

    #     --prefix=/usr                                       \

    #     --foobar-options

    # CT_DoExecLog ALL make

    # CT_DoExecLog ALL make DESTDIR="${CT_SYSROOT_DIR}" install

    # CT_Popd

    :

}