[U-Boot] Falcon mode boot support

[Andy Pont]

Hi Tom,

Following the experiment that yielded the following results:

> U-Boot> time sf read ${loadaddr} 0x200000 ${loadsize}
> 
> I get the following back:
> 
> SF: 2541352 bytes @ 0x200000 Read: OK
> time: 2.447 seconds

I have done some reading and poking around and have added the
OMAP3_MCSPI_CHCONF_TURBO flag to the SPI channel enablement in the
omap3_spi_read() function within omap3_spi.c and now the same command takes
1.279 seconds to execute.

I have also added a couple of printf() statements around the call to read
the flash device that loads the kernel image in spi_load_image_os() and the
timestamps on the output to the serial console consistently show that it is
taking around 3.5 seconds to load the same kernel image.

I haven't fully looked into what is going on as I haven't yet found the full
call path from spi_flash_read() in spi_flash.h to when it eventually results
in the call to omap3_spi_read() and so it may be doing more and I'm not
actually comparing apples with apples.

Could you (or maybe Jagannadha as SPI custodian) point me in the right
direction?

Thanks,

Andy.