sf: Tidy up public and private header files

Since spi_flash.h is supposed to be the public API for SPI flash, move
private things to sf_internal.h. Also tidy up a few comment nits.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Jagannadha Sutradharudu Teki <jagannadh.teki@gmail.com>
9 files changed