relocate_sdk: Skip to do relocation if the file size is less than 64 byte

relocate_sdk: Skip to do relocation if the file size is less than 64 byte

When toolchain directory is changed to execute mode, some non-executable
files or empty files are sorted. This will lead to the below error:

	Extracting SDK...done
	Setting it up...Traceback (most recent call last):
	  File "..._SDK/relocate_sdk.py", line 208, in <module>
	    arch = get_arch()
	  File "..._SDK/relocate_sdk.py", line 39, in get_arch
	    ei_mag0,ei_mag1_3,ei_class = struct.unpack("<B3sB11x", e_ident)
	struct.error: unpack requires a string argument of length 16

To call get_arch and parse_elf_header, we should ensure the sorted file
is bigger than 64 byte.

Signed-off-by: Roy Li <rongqing.li@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>