As for _TEXT_BASE vs TEXT_BASE, this is normal: TEXT_BASE is the image base, and _TEXT_BASE is the address of a variable holding the value of TEXT_BASE, so it's not surprising that they are not equal.
As for your problem: your reports show that start.S sets r10 and r9 as expected, but that board_init_f does not contain the pic prolog code. I wonder if you may have built it without -fPIC or -fPIE. Normally with -fPIE/PIC you should have seen board_init_f (and any function) start with something like:
c1080690: e59fa120 ldr sl, [pc, #288] ; c10807b8 <board_init_f+0x128> c1080694: e08fa00a add sl, pc, sl
Can you check the build logs to see which options were applied to lib/arm/board.c?
I'll try with your CodeSourcery toolchain (I'm using the ELDK 4.2 one), but there is no reason why it would not be EABI compliant.
Amicalement,