kconfig: Restore missing custom changes + add patches

kconfig: Restore missing custom changes + add patches

Commit 6eacea5ae0 accidentally removed these changes in merge_config.sh:
0f56304521 ("merge_config.sh: create temporary files in /tmp")
28fac3973b ("merge_config.sh: add br2-external support")

Changes were lost because commits just changed files, but didn't add patches.
Therefore not only restore our changes, but also add (updated) patches.

Missing 0f56304521 caused breaking merge_config.sh when used in out of
tree build:
$ make -C buildroot O=$PWD/output defconfig
...
$ cd output
$ echo 'BR2_TARGET_GENERIC_HOSTNAME="test"' > test.frag
$ ../buildroot/support/kconfig/merge_config.sh .config test.frag
Using .config as base
Merging test.frag
umask 0022 && make -C /home/test/buildroot O=/home/test/output/. alldefconfig
  GEN     /home/test/output/Makefile
*** Can't read seed configuration "./.tmp.config.qIcpASpUyh"!
make[1]: *** [Makefile:925: alldefconfig] Error 1
make: *** [Makefile:16: _all] Error 2

Fixes: 6eacea5ae0 support/kconfig: bump to kconfig from Linux 4.17-rc2
Signed-off-by: Petr Vorel <petr.vorel@gmail.com>
Reported-by: Erico Nunes <nunes.erico@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>