Add SPI-MEM framework ...

This framework supports SPI operations using a common
spi_mem_op structure:
 - command
 - addr
 - dummy
 - data

The framework manages SPI bus configuration:
 - speed
 - bus width (Up to quad mode)
 - chip select

Change-Id: Idc2736c59bfc5ac6e55429eba5d385275ea3fbde
Signed-off-by: Lionel Debieve <lionel.debieve@st.com>
Signed-off-by: Christophe Kerello <christophe.kerello@st.com>