ARM: imx_v6_v7_defconfig: Remove firmware loader helper

Testing on a imx6dl board with a QCA9377 SDIO Wifi chip shows that the
QCA9377 firmware takes more than three minutes to start getting loaded,
which is a very inconvenient behavior.

CONFIG_FW_LOADER_USER_HELPER and CONFIG_FW_LOADER_USER_HELPER_FALLBACK
were selected by commit 30fdd51b ("ARM: imx_v6_v7_defconfig:
add CONFIG_FW_LOADER_USER_HELPER")

By removing the CONFIG_FW_LOADER_USER_HELPER and
CONFIG_FW_LOADER_USER_HELPER_FALLBACK options the QCA9377 firmware is
loaded around 10 seconds after boot, which is the expected behavior.

The motivation for commit 30fdd51b ("ARM: imx_v6_v7_defconfig:
add CONFIG_FW_LOADER_USER_HELPER") was related to loading the SDMA
firmware,and at the time of that commit, the SDMA driver was loaded
as built-in.

Now that the SDMA driver is selected as a kernel module, its firmware can
be successfully loaded as well without the need of
CONFIG_FW_LOADER_USER_HELPER and CONFIG_FW_LOADER_USER_HELPER_FALLBACK.

Remove the selection of these two options.

Also, successfully tested the loading of the VPU firmware without
these options.

Signed-off-by: Fabio Estevam <festevam@gmail.com>
Tested-by: Otavio Salvador <otavio@ossystems.com.br>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>