ARM: imx_v6_v7_defconfig: add DMATEST support

Add DMATEST support and remove invalid options, such as
CONFIG_BT_HCIUART_H4 is default enabled and CONFIG_SND_SOC_IMX_WM8962
is out of date and not appear in any config file. Please refer to
Documentation/driver-api/dmaengine/dmatest.rst to test MEMCPY feature
of imx-sdma.

Signed-off-by: Robin Gong <yibin.gong@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>