ARM: ux500: Remove u9540.dts as it's been replaced

This must have been a merge error. There was a patch which renamed the
u9540.dts to ccu9540.dts, however the u9540.dts was reincarnate with
the same patches which created it in the first place. Let's kill it
once and for all.

Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@stericsson.com>