[U-Boot] [PATCH 3/4] x86: doc: Mention qemu-x86_64 support

[Bin Meng]

Currently only 32-bit U-Boot for QEMU x86 is documented. Mention
the 64-bit support.

Signed-off-by: Bin Meng <bmeng.cn at gmail.com>
---

 doc/README.x86 | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/doc/README.x86 b/doc/README.x86
index 8cc4672..ab48466 100644
--- a/doc/README.x86
+++ b/doc/README.x86
@@ -32,7 +32,7 @@ are supported:
    - Link (Chromebook Pixel)
    - Minnowboard MAX
    - Samus (Chromebook Pixel 2015)
-   - QEMU x86
+   - QEMU x86 (32-bit & 64-bit)
 
 As for loading an OS, U-Boot supports directly booting a 32-bit or 64-bit
 Linux kernel as part of a FIT image. It also supports a compressed zImage.
@@ -376,7 +376,9 @@ QEMU x86 target instructions for bare mode:
 
 To build u-boot.rom for QEMU x86 targets, just simply run
 
-$ make qemu-x86_defconfig
+$ make qemu-x86_defconfig (for 32-bit)
+or
+$ make qemu-x86_64_defconfig (for 64-bit)
 $ make all
 
 Note this default configuration will build a U-Boot for the QEMU x86 i440FX
@@ -387,6 +389,8 @@ Device Tree Control  --->
 	...
 	(qemu-x86_q35) Default Device Tree for DT control
 
+To run 64-bit U-Boot, qemu-system-x86_64 should be used instead.
+
 Test with coreboot
 ------------------
 For testing U-Boot as the coreboot payload, there are things that need be paid
-- 
2.7.4