ARM: imx_v6_v7_defconfig: Select HCIUART_H4

The old warp board revision had hardware issues that prevented
the RTS/CTS lines to work with the Bluetooth module.

Tha latest rev1.12 fixes this problem, so now we should better use
CONFIG_BT_HCIUART_H4 instead, as it provides a better throughput than
the CONFIG_BT_HCIUART_3WIRE option.

Suggested-by: Arthur Lambert <arthur@dreem.com>
Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>