console: Fix pre-console flushing via cfb_console being very slow

On my A10 OlinuxIno Lime I noticed a huge (5+ seconds) delay coming from
console_init_r. This turns out to be caused by the preconsole buffer flushing
to the cfb_console. The Lime only has a 16 bit memory bus and that is already
heavy used to scan out the 1920x1080 framebuffer.

The problem is that print_pre_console_buffer() was printing the buffer once
character at a time and the cfb_console code then ends up doing a cache-flush
for touched display lines for each character.

This commit fixes this by first building a 0 terminated buffer and then
printing it in one puts() call, avoiding unnecessary cache flushes.

This changes the time for the flush from 5+ seconds to not noticable.

The downside of this approach is that the pre-console buffer needs to fit
on the stack, this is not that much to ask since we are talking about plain
text here. This commit also adjusts the sunxi CONFIG_PRE_CON_BUF_SZ to
actually fit on the stack. Sunxi currently is the only user of the pre-console
code so no other boards need to be adjusted.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Tom Rini <trini@konsulko.com>

include/configs/sunxi-common.h

@@ -336,7 +336,7 @@ extern int soft_i2c_gpio_scl;
 
 /* Enable pre-console buffer to get complete log on the VGA console */
 #define CONFIG_PRE_CONSOLE_BUFFER
-#define CONFIG_PRE_CON_BUF_SZ		(1024 * 1024)
+#define CONFIG_PRE_CON_BUF_SZ		4096 /* Aprox 2 80*25 screens */
 /* Use the room between the end of bootm_size and the framebuffer */
 #define CONFIG_PRE_CON_BUF_ADDR		0x4f000000