DFU: Accept redundant spaces and tabs in dfu_alt_info

DFU: Accept redundant spaces and tabs in dfu_alt_info

If dfu_alt_info has repeated spaces or tab (for indentation or
readability), the dfu fails to parse it. For example, if
dfu_alt_info="mtd nor1=image raw  100000 200000" (double spaces
after "raw"), the image entity start address is '0' and the size
'0x100000'. This is because the repeated space is not skipped.

Use space and tab as a separater and apply skip_spaces() to
skip redundant spaces and tabs.

Signed-off-by: Masami Hiramatsu <masami.hiramatsu@linaro.org>