scripts/functions: introduce target_bits_32 and target_bits_64 variables

These variables behave the same for bitness as their counterparts do
for endianness: they are defined to the appropriate bitness.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Cody P Schafer <dev@codyps.com>

CT_EXPERIMENTAL=y

CT_LOCAL_TARBALLS_DIR="${HOME}/src"

CT_SAVE_TARBALLS=y

CT_LOG_EXTRA=y

CT_ARCH_CPU="cpu32"

CT_ARCH_m68k=y

CT_ARCH_BINFMT_FLAT=y

CT_BINUTILS_V_2_20_1a=y

CT_CC_V_4_3_4=y

CT_LIBC_none=y

CT_GMP_V_4_3_2=y

CT_MPFR_V_2_4_2=y