atheros[ar2315]: don't detect flash size during board initialization

atheros[ar2315]: don't detect flash size during board initialization

We should not detect actual flash size during board initialization to
find board config at the end of the flash, just use large enough mapping
size (currently 128 mbit). If mapping size is larger than the actual
flash size, than flash will simply be mapped multiple times. This change
simplifies code by removing duplication and saves about 200 bytes of
uncompressed kernel :)

Tested with Ubnt LS2 board equipped with STM 25p32v6p NOR flash (32 mbit).

Signed-off-by: Sergey Ryazanov <ryazanov.s.a@gmail.com>
git-svn-id: svn://svn.openwrt.org/openwrt/trunk@41317 3c298f89-4303-0410-b956-a3cf2f4a3e73