configs: migrate CONFIG_SYS_ARM_CACHE_* in Kconfig

Move CONFIG_SYS_ARM_CACHE_WRITETHROUGH and
CONFIG_SYS_ARM_CACHE_WRITEALLOC into Kconfig done by moveconfig.py.

Kconfig uses a choice between the 3 values supported in U-Boot,
including the new configuration CONFIG_SYS_ARM_CACHE_WRITEBACK
(the default configuration).

The patch also avoids to select simultaneously 2 configurations.

Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>