linux-g2c: Fix location of g2c-common patches

The patches which are common to all g2c must to be placed at 'g2c'
directory. Move them.

Fixes:

,----
| WARNING: Unable to get checksum for linux-g2c SRC_URI entry
|     0003-ARM-7668-1-fix-memset-related-crashes-caused-by-rece.patch:
|     [Errno 2] No such file or directory:
|     '.../build/downloads/0003-ARM-7668-1-fix-memset-related-crashes-caused-by-rece.patch'
`----

Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>
linux-g2c: Simplify recipe as it has a single version

As we have a single version we don't need to use a .inc file.
Specially as this kernel recipe is very simple and the .inc file ends
adding complexity where there is no need for it.

This also rework the recipe for easy maintenance and cleanness.

Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>
g2c-base.inc: Remove duplicated code from mxs-base.inc

The g2c machines are based on the MXS SoC family and we should reuse
the mxs-base.inc file for easy maintenance and to avoid duplicating
code.

Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>