ARM: shmobile: Remove GENERIC_PHY from shmobile_defconfig

Remove the GENERIC_PHY config option from shmobile_defconfig, as it is
selected by PHY_RCAR_GEN3_USB2.

PHY_RCAR_GEN3_USB2 is enabled by the commit 0cd4f4f1
("ARM: shmobile: Enable PHY_RCAR_GEN3_USB2 in shmobile_defconfig").

Signed-off-by: Biju Das <biju.das@bp.renesas.com>
Acked-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>