stv0991: Add basic stv0991 architecture support

stv0991 architecture support added. It contains the support for
following blocks
- Timer
- uart

Signed-off-by: Vikas Manocha <vikas.manocha@st.com>
[trini: Add arch/arm/cpu/armv7/Makefile hunk]
Signed-off-by: Tom Rini <trini@ti.com>