uqmi: use -ffunction-sections and --gc-sections, reduces binary size from 57k to 29k

Signed-off-by: Felix Fietkau <nbd@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@41051 3c298f89-4303-0410-b956-a3cf2f4a3e73