Change objcopy's --set-section-alignment option so that it takes a byte...

Change objcopy's --set-section-alignment option so that it takes a byte alignment value rather than a power of two alignment value.

	PR 24942
	* objcopy.c (copy_usage): Update description of
	--set-section-alignment.
	(copy_main): Interpret numeric argument of --set-section-alignment
	as a byte alignment, not a power of two alignment.
	* doc/binutils.texi: Update description of
	--set-section-alignment.
	* testsuite/binutils-all/set-section-alignment.d: New test.
	* testsuite/binutils-all/objcopy.exp: Run the new test.