MALI: midgard: RK: add separate src dir of Midgard driver for RK Linux device

MALI: midgard: RK: add separate src dir of Midgard driver for RK Linux device

The version of Midgard DDK used in RK Linux device is different from the one
used in Android platforms.
It might be convenient to have a separate src directory for it.

The new directory drivers/gpu/arm/midgard_for_linux is copied from
drivers/gpu/arm/midgard of commit 206f372ede.
It's on DDK r9p0-05rel0
There are also a few modifications in some 'Kbuild' files.

A new config MALI_MIDGARD_FOR_LINUX is introduced to specify which directory
of Midgard to use.
If defined, kbuild will compile src files under
drivers/gpu/arm/midgard_for_rk_linux_device,
otherwise, drivers/gpu/arm/midgard.

There is already a source directory of Midgard driver,
the 'Kconfig' file of the new directory is not be involved
in kconfig process.
Otherwise, there are problems caused by configs
with the same names in the two directories.
So, "midgard_for_rk_linux_device" could not be configured via menuconfig.

In the new directory, all the default configs are defined in default_config.mk.
'Kbuild' files include it.

Change-Id: I54f61cc50f7a168a742db7a11c6b6eebe21528f8
Signed-off-by: chenzhen <chenzhen@rock-chips.com>
Signed-off-by: Jacob Chen <jacob2.chen@rock-chips.com>