[U-Boot] common/xyzmodem.c, ymodem, slow behavior receiving bytes

[Angelo Dureghello]

Dear all,

i have found out that this issue was also and probably mainly caused 
from the issue fixed in my last patch posted:

http://patchwork.ozlabs.org/patch/201421/

All serial driver routines (for mcfuart.c in my case) was executed
from the flash memory, even after monitor relocation to ram.

Considering flash memory access time (10 wait states set in my case), 
this was causing code execution speed to be dramatically slow, near the 
limit for receiving at 115200 uart speed.

Enabling cache for the sdram fasted up a bit the operations and solved 
the issue, but main problem here was certainly the execution from flash.

Best Regards
Angelo Dureghello