README.arm-relocation: get relocated address in gdb

When your emulator is connected at reset (or is used to load u-boot)
it is possible to get the relocation address from the gd->relocaddr
since gd is always in r8 (on ARM) it is addressable before the
gdb has remapped symbols.

Document this alternate method in-line with the original method
written by Heiko Schocher.

Signed-off-by: Ben Gardiner <bengardiner@nanometrics.ca>
CC: Heiko Schocher <hs@denx.de>
CC: Wolfgang Denk <wd@denx.de>
Acked-by: Heiko Schocher <hs@denx.de>

doc/README.arm-relocation

@@ -164,6 +164,7 @@ Program received signal SIGSTOP, Stopped (signal).
 add-symbol-file u-boot 0x8ff08000
 		       ^^^^^^^^^^
 		       get this address from u-boot bdinfo command
+		       or get it from gd->relocaddr in gdb
 
  => bdinfo
 rch_number = XXXXXXXXXX
@@ -182,4 +183,11 @@ irq_sp      = XXXXXXXXXX
 sp start    = XXXXXXXXXX
 FB base     = XXXXXXXXXX
 
+or interrupt execution by any means and re-load the symbols at the location
+specified by gd->relocaddr -- this is only valid after board_init_f.
+
+(gdb) set $s = gd->relocaddr
+(gdb) symbol-file
+(gdb) add-symbol-file u-boot $s
+
 Now you can use gdb as usual :-)