bootconfig: Cleanup dummy headers in tools/bootconfig

Cleanup dummy headers in tools/bootconfig/include except
for tools/bootconfig/include/linux/bootconfig.h.
For this change, I use __KERNEL__ macro to split kernel
header #include and introduce xbc_alloc_mem() and
xbc_free_mem().

Link: https://lkml.kernel.org/r/163187299574.2366983.18371329724128746091.stgit@devnote2

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

tools/bootconfig: Fix a build error accroding to undefined fallthrough

Since the "fallthrough" is defined only in the kernel, building
lib/bootconfig.c as a part of user-space tools causes a build
error.

Add a dummy fallthrough to avoid the build error.

Link: https://lkml.kernel.org/r/162087519356.442660.11385099982318160180.stgit@devnote2

Cc: Ingo Molnar <mingo@kernel.org>
Cc: stable@vger.kernel.org
Fixes: 4c1ca831adb1 ("Revert "lib: Revert use of fallthrough pseudo-keyword in lib/"")
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

tools: bootconfig: Add bootconfig command

Add "bootconfig" command which operates the bootconfig
config-data on initrd image.

User can add/delete/verify the boot config on initrd
image using this command.

e.g.
Add a boot config to initrd image
# bootconfig -a myboot.conf /boot/initrd.img

Remove it.
# bootconfig -d /boot/initrd.img

Or verify (and show) it.
# bootconfig /boot/initrd.img

Link: http://lkml.kernel.org/r/157867223582.17873.14342161849213219982.stgit@devnote2

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
[ Removed extra blank line at end of bootconfig.c ]
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>