eco32: preserve IEN flags

When restoring PSW, the IEN flags should be masked out.
This also fix a bug in SET_PSW, which would only preserve
the 8 lsb instead of the full 16-bit.

Signed-off-by: Stefan Kristiansson <stefan.kristiansson@saunalahti.fi>
eco32: entry: only do_work_pending when returning to user mode

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