Remove data_abort_handler from ARM crt0 files.

This causes data_abort_handler from lib/unwarminder/safe_read.S to be
used instead. It allows unwarminder to avoid data aborts when
displaying the backtrace. A data_abort_handler remains in system-arm.c,
but it is not used because it is declared as a weak symbol.

Change-Id: I832066ed514347fe697e219872e90fbdd937f477
Reviewed-on: http://gerrit.rockbox.org/475
Reviewed-by: Marcin Bukat <marcin.bukat@gmail.com>
Tested-by: Boris Gjenero <boris.gjenero@gmail.com>

firmware/target/arm/pnx0101/crt0-pnx0101.S

@@ -203,11 +203,6 @@ fiq_handler:
     ldmfd sp!, {r0-r7, r12, lr}
     subs pc, lr, #4
 
-data_abort_handler:
-    sub    r0, lr, #8 
-    mov    r1, #2
-    b      UIE
-
 irq_handler:
 #ifndef STUB
     stmfd  sp!, {r0-r11, r12, lr}

firmware/target/arm/pp/crt0-pp.S

@@ -402,11 +402,6 @@ prefetch_abort_handler:
     mov    r1, #1
     b      UIE
 
-data_abort_handler:
-    sub    r0, lr, #8
-    mov    r1, #2
-    b      UIE
-
 /* Align stacks to cache line boundary */
     .balign 32
 

firmware/target/arm/pp/crt0-pp502x-bl-usb.S

@@ -351,11 +351,6 @@ prefetch_abort_handler:
     mov     r1, #1
     b       UIE
 
-data_abort_handler:
-    sub     r0, lr, #8 
-    mov     r1, #2
-    b       UIE
-
 /* should never happen in the bootloader */
 fiq_handler:
     subs    pc, lr, #4