a320evb: fix udelay / __udelay confusion

Fix the following compiler problems:

arch/arm/cpu/arm920t/a320/liba320.a(timer.o): In function `udelay':
/home/wd/git/u-boot/work/arch/arm/cpu/arm920t/a320/timer.c:160: multiple definition of `udelay'
lib/libgeneric.a(time.o):/home/wd/git/u-boot/work/lib/time.c:34: first defined here
lib/libgeneric.a(time.o): In function `udelay':
time.c:(.text+0x1c): undefined reference to `__udelay'

Signed-off-by: Wolfgang Denk <wd@denx.de>