ddr: socfpga: Fix EMIF clear timeout

ddr: socfpga: Fix EMIF clear timeout

The current EMIF clear timeout handling code was applying bitwise
operations to signed data types and as it was, was extremely hard
to read. Replace it with simple wait_for_bit(). Expand the error
handling to make it more readable too.

This patch also changes the timeout for emif_clear() from 14 hours
to 1 second.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Chin Liang See <chin.liang.see@intel.com>
Cc: Dinh Nguyen <dinguyen@kernel.org>
Cc: Simon Goldschmidt <simon.k.r.goldschmidt@gmail.com>
Cc: Tien Fong Chee <tien.fong.chee@intel.com>