ARM: shmobile: Enable R-Car Gen 2 PCIe in shmobile_defconfig

The R-Car Gen 2 PCIe driver provides PCIe host support for
Renesas R-Car Gen2 platforms. To increase hardware support enable
the driver in the shmobile_defconfig multiplatform configuration.

Cc: Phil Edworthy <phil.edworthy@renesas.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>