kconfig: rename the defconfig and olddefconfig targets

What 'defconfig' really does is save the current .config to a defconfig,
so it is better named 'savedefconfig' (as other projects do).

What 'olddefconfig' really does is create a .config from a defconfig,
so rename it to 'defconfig' (as other projects do, too).

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>

CT_EXPERIMENTAL=y

CT_LOCAL_TARBALLS_DIR="${HOME}/src"

CT_SAVE_TARBALLS=y

CT_LOG_EXTRA=y

CT_ARCH_s390=y

CT_KERNEL_linux=y

CT_KERNEL_V_2_6_31_14=y

CT_BINUTILS_V_2_20_1a=y

CT_CC_V_4_3_4=y

CT_CC_LANG_CXX=y

CT_LIBC_glibc=y

CT_LIBC_GLIBC_V_2_9=y

CT_GMP_V_4_3_2=y

CT_MPFR_V_2_4_2=y