cfi_flash driver - Add delay after reset command

I ran into a problem where the reset was failing except when I enabled
debugging support.  After talking with Garret Swalling at Spansion I
was told that the GL-N series of devices require a 500ns wait for the
reset to complete.  The below patch adds a 1us delay after all reset
commands.

-Aaron Williams

Signed-off-by: Aaron Williams <aaron.williams@caviumnetworks.com>
Signed-off-by: Stefan Roese <sr@denx.de>