tzdata: Add bbappend to setup writable conf files

:Release Notes:
Allow changing the time zone when rootfs is read-only by having
/etc/localtime and /etc/timezone be symlinks to files under
/var/luna/preferences.

:Testing Performed:
Verified that:
- symlinks in /etc points to /var/luna/preferences
- /var/luna/preferences/localtime point to
  /usr/share/zoneinfo/Universal
- /var/luna/preferences/timezone contains Universal

:QA Notes:

:Issues Addressed:
[GF-44351] luna-sysservice can't change time zone when rootfs is
           read-only
[GF-51667] CCC: tzdata=webos1

Open-webOS-DCO-1.0-Signed-off-by: Nikolay Orliuk <nikolay.orliuk@lge.com>
Change-Id: Ie8c9d6067fce57911796953483e5f6e0efb98fad
Reviewed-on: https://g2g.palm.com/3769
Reviewed-by: DCO Verification
Reviewed-by: Herb Kuta <herb.kuta@lge.com>
Reviewed-by: Joungyong Choi <joungyong.choi@lge.com>
Tested-by: Joungyong Choi <joungyong.choi@lge.com>