ARM: cache-tauros2: remove ARMv6 code

When building a kernel with support for both ARMv6 and ARMv7 but
no MMU, the call from tauros2_internal_init to adjust_cr causes
a link error. While that could probably be resolved, we don't
actually support cache-tauros2 on ARMv6 any more. All PJ4 CPU
implementations support both ARMv6 and ARMv7 and we already assume
that we are using them only in ARMv7 mode.

Removing the ARMv6 code path reduces the code size and avoids
the linker error.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Haojian Zhuang <haojian.zhuang@gmail.com>