infra/pkg-kconfig: Be sure to reconfigure the package on foo-reconfigure

Currently, calling foo-reconfigure for a kconfig-based package will not
re-trigger the configuration (kconfig-wise) step for the package.

This can be problematic when using an override-srcdir suring development
and the content of the veride-srcdir changes (e.g. on a rebase, a merge,
or during a bisect).

This is because the configuration (kconfig-wise) of the package is not
done in the _CONFIGURE_CMDS block, but as a separate action that is not
part of any step [0].

So, be sure to remove the stamp file .stamp_kconfig_fixup_done during
the foo-clean-for-reconfigure rule, so that the configuration is applied
again with the new source tree.

We use another rule, foo-clean-kconfig-for-reconfigure, because we do
not want to override the default foo-clean-for-reconfigure rule, and we
have no way to add conditional commands to it.

[0] The reasons it was not done are not entirely clear in my head, but
IIRC that was not working at the time we tried with Thomas DS.

Reported-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Cc: Thomas De Schampheleire <patrickdepinguin@gmail.com>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Tested-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Reviewed-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>