nios2: default CONFIG_NIOS2_BOOT_LINK_OFFSET to 8MB

Signed-off-by: Ley Foon Tan <lftan@altera.com>

arch/nios2/configs/3c120_defconfig

@@ -22,6 +22,7 @@ CONFIG_NIOS2_DCACHE_SIZE=0x8000
 CONFIG_NIOS2_ICACHE_SIZE=0x8000
 # CONFIG_NIOS2_CMDLINE_IGNORE_DTB is not set
 CONFIG_NIOS2_PASS_CMDLINE=y
+CONFIG_NIOS2_BOOT_LINK_OFFSET=0x00800000
 CONFIG_NET=y
 CONFIG_PACKET=y
 CONFIG_UNIX=y