x86: fsp: Add comments about U-Boot entering start.S twice

Add some comments in start.S for the fact that with FSP U-Boot
actually enters the code twice. Also change to use fsp_init()
and fsp_continue for accuracy.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Acked-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 687208f..273f08f 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -229,7 +229,7 @@
 	depends on HAVE_FSP
 	default 0x2000000
 	help
-	  Stack top address which is used in FspInit after DRAM is ready and
+	  Stack top address which is used in fsp_init() after DRAM is ready and
 	  CAR is disabled.
 
 config FSP_SYS_MALLOC_F_LEN