Remove CONFIG_USE_STDINT

You do not need to use the typedefs provided by compiler.

Our compilers are either IPL32 or LP64.  Hence, U-Boot can/should
always use int-ll64.h typedefs like Linux kernel, whatever the
typedefs the compiler internally uses.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>