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

Signed-off-by: Alexey Zaytsev <alexey.zaytsev@gmail.com>

src/drivers/bitbash/spi_bit.c

@@ -22,7 +22,7 @@
 #include <byteswap.h>
 #include <errno.h>
 #include <assert.h>
-#include <timer.h>
+#include <unistd.h>
 #include <gpxe/bitbash.h>
 #include <gpxe/spi_bit.h>