arch: use the newly introduced target_bits_64

Convert MIPS and Sparc over to using the new target_bits_64 variable.

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

 reporter_name="Benoît Thébaudeau"

 reporter_url="http://www.advansee.com/"

 reporter_comment="Cortex-A9 with NEON support using the hard-float GNU EABI."