clk: tango4: rename ARCH_TANGOX to ARCH_TANGO

Requested by arm-soc maintainer Kevin Hilman in v9 review.
http://article.gmane.org/gmane.linux.ports.arm.kernel/456331



Signed-off-by: Marc Gonzalez <marc_gonzalez@sigmadesigns.com>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>