clang-format: Use llvm sort include rules

We do not need to specify own rules, as we basically use llvm
include style.
ref: https://llvm.org/docs/CodingStandards.html#include-style



Move SortIncludes to the place where it was (I am fixing all other
projects, where we just change one line, no move required).

Signed-off-by: Martin Kojtal <martin.kojtal@arm.com>