Build support for generic driver on HiKey.

Reviewed-by: Pascal Brand <pascal.brand@linaro.org>
Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>

This config is required to prevent errors on boot like below when using
https://github.com/96boards-hikey/linux

 hikey-mainline-rebase branch:

ssp-pl022 f7106000.spi: could not find pctldev for node /soc/pinmux@f7010000/spi0_pmx_func, deferring probe
gpiochip_add: GPIOs 480..487 (f8014000.gpio) failed to register

Signed-off-by: Victor Chong <victor.chong@linaro.org>
Reviewed-by: Jens Wiklander <jens.wiklander@linaro.org>
Reviewed-by: Joakim Bech <joakim.bech@linaro.org>
Reviewed-by: Jerome Forissier <jerome.forissier@linaro.org>

- Kernel config fragments that were used by the QEMU makefile are
merged into kconfigs/qemu.conf. Now, each platform has its own file
in kconfigs/
- All platforms: CONFIG_DMA_SHARED_BUFFER cannot be enabled directly
because it is  a not a visible symbol (has no prompt in Kconfig).
CONFIG_DRM is set instead which depends on DMA.
- kconfigs/hikey.conf: keep only what is necessary

Signed-off-by: Jerome Forissier <jerome.forissier@linaro.org>
Tested-by: Jerome Forissier <jerome.forissier@linaro.org> (FVP, HiKey)
Reviewed-by: Joakim Bech <joakim.bech@linaro.org>
Tested-by: Joakim Bech <joakim.bech@linaro.org> (QEMU, MTK8173)