bcm2708_fb: Disable warning when calling dma_alloc_coherent

When we boot the kernel on the rpi4/3/2, we sometimes could see the
warning calltrace like below:

bcm2708_fb soc:fb: FB found 1 display(s)
cma: cma_alloc: alloc failed, req-size: 1753 pages, ret: -12
WARNING: CPU: 2 PID: 1 at mm/page_alloc.c:4702 __alloc_pages_nodemask+0x284/0x2c8
Modules linked in:
CPU: 2 PID: 1 Comm: swapper/0 Not tainted 5.3.0-1013-raspi2 #15-Ubuntu
Hardware name: Raspberry Pi 3 Model B Plus Rev 1.3 (DT)
pstate: 20400005 (nzCv daif +PAN -UAO)
pc : __alloc_pages_nodemask+0x284/0x2c8
lr : __dma_direct_alloc_pages+0x100/0x1e8
sp : ffff0000100238a0
x29: ffff0000100238a0 x28: 0000000000000000
x27: ffffa7c578867580 x26: ffffa7c57786a080
...

After investigation, I found there are two situations which could
introduce this calltrace.
 1) booting the arm64 kernel on rpi4 boards without the monitor
 connected, in this situation, the xres and yres euqal to 0, so the
 dma_alloc_coherent wants to alloc a memory region with 0 size, this
 will result the get_order() returns (BITS_PER_LONG - PAGE_SHIFT),
 then it will introduce the calltrace because
 unlikely(order >= MAX_ORDER) is true (mm/page_alloc.c)
 2) booting the kernel on rpi2/3 boards with a high resolution monitor
 connected, in this case the xres * yres is too big, the cma_alloc
 doens't have enough memory for it, and finally it will also introduce
 the calltrace by unlikely(order >= MAX_ORDER) is true.

The bcm2708_fb could handle the situation of failure on calling
dma_alloc_coherent, and the driver itself will print some log to
notify users that this alloc fails. So we don't need the mm/page_alloc
to print that calltrace anymore, printing a calltrace when booting
usually makes users think the kernel has a critical problem.

Signed-off-by: Hui Wang <hui.wang@canonical.com>

drivers/video/fbdev/bcm2708_fb.c

@@ -410,7 +410,8 @@ static int bcm2708_fb_set_par(struct fb_info *info)
 		}
 
 		fb->cpuaddr = dma_alloc_coherent(info->device, image_size,
-						 &fb->dma_addr, GFP_KERNEL);
+						 &fb->dma_addr,
+						 GFP_KERNEL | __GFP_NOWARN);
 
 		if (!fb->cpuaddr) {
 			fb->dma_addr = 0;