ARM: davinci: fix cache flush build error

The TNET variant of DaVinci compiles some code that it shares
with other DaVinci variants, however it has a V6 CPU rather than
an ARM926T, thus the hardcoded call to arm926_flush_kern_cache_all()
in sleep.S will obviously fail, and we need to build with the
v6_flush_kern_cache_all() call instead. This was triggered by
manually altering the DaVinci config to build the TNET version.

Cc: Dave Martin <dave.martin@linaro.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Sekhar Nori <nsekhar@ti.com>
Cc: stable@kernel.org