populate_sdk_base: improve POSIXLY_CORRECT compat

populate_sdk_base: improve POSIXLY_CORRECT compat

The install script is sometimes called under POSIXLY_CORRECT. This
requires two fixes be made:

1. `find -perm /0000` is a gnuism; replace with an equivalent boolean
expression using `-perm -0000`.

2. POSIX grep requires that all options be passed on the command line
before all files; otherwise, the options must be parsed as filenames.

Signed-off-by: Richard Tollerton <rich.tollerton@ni.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>