dropbear: update to 2012.55 and refresh patches

Upstream has a few code cleanups, more eagerly burns sensitive memory and
includes the fix for CVE-2012-0920. Full changelog:
https://matt.ucc.asn.au/dropbear/CHANGES



Local changes:
- Removed PKG_MULTI which is no longer in options.h (even before 2011.54)
- Merged DO_HOST_LOOKUP into 120-openwrt_options.patch
- Removed LD from make opts (now included in TARGET_CONFIGURE_OPTS)
- Removed 400-CVE-2012-0920.patch which is included in 2012.55

Signed-off-by: Catalin Patulea <cat@vv.carleton.ca>
Signed-off-by: Florian Fainelli <florian@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@34496 3c298f89-4303-0410-b956-a3cf2f4a3e73