GitHub usage documentation

Signed-off-by: Pascal Brand <pascal.brand@st.com>
Removed unused KTA related defines

- Moved IO macro from kta_mem.h to io.h.
- Removed unused TEE_MEM_xyz defines.
- Removed code that was used for TA's in TEE RAM (impossible to reach
  that code).

Signed-off-by: Joakim Bech <joakim.bech@linaro.org>
Removed file core/include/kernel/kta_mem.h

Signed-off-by: Joakim Bech <joakim.bech@linaro.org>
Adding GlobalPlatform documentation

Signed-off-by: Joakim Bech <joakim.bech@linaro.org>