tools: fix define2mk.sed to not add quotes around negative integers

tools: fix define2mk.sed to not add quotes around negative integers

The sed script, tools/scripts/define2mk.sed, converts config defines
from C headers into include/autoconf.mk for the use in Makefiles.

I found the tool adds quotes around negative integer values.

For example, at the point of the v2016.07-rc1 tag,
include/configs/microblaze-generic.h defines
  #define CONFIG_BOOTDELAY         -1     /* -1 disables auto-boot */

Because it is an integer option, it should be converted to:
  CONFIG_BOOTDELAY=-1

But, the script actually converts it to:
  CONFIG_BOOTDELAY="-1"

This is a fatal problem for the tools/moveconfig.py because it parses
include/autoconf.mk for the config defines from the board headers.
CONFIG_BOOTDELAY="-1" is considered as a string type option and it
is dropped due to the type mismatch from the entry in Kconfig.

This commit fixes the script so that the tools/moveconfig.py can
correctly convert integer options with a negative value.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>