Windows does not have a standard getopt implementation. To address
this an equivalent implementation has been provided in win_posix.c
However, the implementation has an issue with option processing as
described below.

Long option names may be abbreviated if the abbreviation is unique
or an exact match for some defined option.
Since some options can be substring of other options e.g. "scp-fw"
option is a substring of "scp-fwu-cfg", we need to identify if an
option is abbreviated and also check for uniqueness. Otherwise if
a user passes --scp-fw as an option, the "scp-fwu-cfg" option may
get selected, resulting in an incorrectly packaged FIP.

This issue has been be fixed by:
  - First searching for an exact match.
  - If exact match was not found search for a abbreviated match.
By doing this an incorrect option selection can be avoided.

Change-Id: I22f4e7a683f3df857f5b6f0783bf9b03a64a0bcc
Signed-off-by: Sami Mujawar <sami.mujawar@arm.com>