greybus: update sysfs documentation files

Impose a few editorial conventions on the Greybus-related sysfs
files under "Documentation".
    - Capitalize "Endo" (except in path names)
    - Capitalize "ID" (except in path names)
    - Use "..." to indicate unspecified path components (because
      ".." means something else).
    - Add the "0x" prior to the "XXXX" representing the Endo ID.

Signed-off-by: Alex Elder <elder@linaro.org>
Reviewed-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>