rcar-gen3: README: Update release information
rcar-gen3: README: Update release information

This commit updates the following information:
- Branch and Commit ID of poky, meta-openembeded.
- Remove information of meta-linaro dependency.

Signed-off-by: Khang Nguyen <8dfb9c771c579920706fa8a68e7ba00c68a28f22@renesas.com>
Signed-off-by: Takamitsu Honda <dd018642994e4b3e742377b6d773664f62294df8@renesas.com>
Change-Id: Idaf1dd51999450a12bb0c6184b1a4f2b050012f1

renesas-rcar/meta-renesas,renesas-rcar/meta-renesas,renesas-rcar/meta-renesas,renesas-rcar/meta-renesas