ti: k3: Setup initial files for platform

Create the baseline Makefile, platform definitions file and platform
specific assembly macros file. This includes first set of constants
for the platform including cache sizes and linker format and a stub for
BL31 and the basic memory layout

K3 SoC family of processors do not use require a BL1 or BL2 binary,
since such functions are provided by an system controller on the SoC.
This lowers the burden of ATF to purely managing the local ARM cores
themselves.

Signed-off-by: Benjamin Fair <b-fair@ti.com>
Signed-off-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Andrew F. Davis <afd@ti.com>