recipes: Replace PR_append with EXTENDPRAUTO_append

:Release Notes:
Non-numeric PR_appends unlike PRINC doesn't provide stable versioning.

:Detailed Notes:
When .bbappend in layer A (with lower BBFILE_PRIORITY) adds
PR_append = "foo1"
and later layer B adds .bbappend for the same recipe with
PR_append = "bar1"
then version goes backward from "1.0-r0foo1" to "1.0-r0bar1foo1".
That's why PRINC was introduced to allow combining multiple .bbappends
while ensuring always increasing overall version, but we're not using
PRINC.

:Testing Performed:
PR_appends are moved to last part of PR, not before numeric value from
PR service or BB_TASKHASH.

:QA Notes:
No change in image.

:Issues Addressed:
[GF-13471] Assign to EXTENDPRAUTO_append instead of PR_append in
           .bbappend-s

Open-webOS-DCO-1.0-Signed-off-by: Martin Jansa <martin.jansa@lge.com>
Change-Id: I045d0433438604c52c8b7cdc0357406aad5daac7
Reviewed-on: https://g2g.palm.com/3156
Reviewed-by: Susan Montooth <susan.montooth@lge.com>
Tested-by: Susan Montooth <susan.montooth@lge.com>