Modify gPXE core and drivers to work with the new timer subsystem

Signed-off-by: Alexey Zaytsev <alexey.zaytsev@gmail.com>
diff --git a/src/drivers/nvs/spi.c b/src/drivers/nvs/spi.c
index be6b590..dbdc32f 100644
--- a/src/drivers/nvs/spi.c
+++ b/src/drivers/nvs/spi.c
@@ -18,7 +18,7 @@
 
 #include <stddef.h>
 #include <errno.h>
-#include <timer.h>
+#include <unistd.h>
 #include <gpxe/spi.h>
 
 /** @file