eco32: remove prom.h

The note in the comment is reality in 3.13, and with that define
gone, our prom.h is completely empty.

Signed-off-by: Stefan Kristiansson <stefan.kristiansson@saunalahti.fi>
eco32: remove remarks in pgtable.h
eco32: remove setup_cpuinfo + add info to show_cpuinfo

Signed-off-by: Stefan Kristiansson <stefan.kristiansson@saunalahti.fi>
eco32: add cpu node to eco32_generic.dts

Signed-off-by: Stefan Kristiansson <stefan.kristiansson@saunalahti.fi>