spi: Remove unused/unnecessary spi_init function definitions

Remove spi_init definitions which:
1. Do nothing
2. Set static global variables to 0

Change-Id: If4c0cdbe2271fc7561becd87ad3b96bd45e77430
Signed-off-by: Furquan Shaikh <furquan@chromium.org>
Reviewed-on: https://review.coreboot.org/20039
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Philippe Mathieu-Daudé <philippe.mathieu.daude@gmail.com>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>

src/southbridge/amd/sb700/spi.c

@@ -35,11 +35,6 @@ static uint32_t get_spi_bar(void)
 	return pci_read_config32(dev, 0xa0) & ~0x1f;
 }
 
-void spi_init(void)
-{
-	/* Not needed */
-}
-
 static void reset_internal_fifo_pointer(void)
 {
 	uint32_t spibar = get_spi_bar();