Add documentation about the interation of the ARM assembler's -EB option and the...

Add documentation about the interation of the ARM assembler's -EB option and the linker's --be8 option.

	PR binutils/18198
	* ld.texinfo (--be8): Add a note about the interaction of this
	option with the assembler's -EB option.

	* doc/c-arm.texi (ARM Options): Add a note about the interaction of
	the -EB option with the linker's --be8 option.