fstools: add direct dependencies on libblobmsg-json and libjson-c

fstools: add direct dependencies on libblobmsg-json and libjson-c

The OpenWrt buildroot ABI version rebuild tracker does not handle
transient dependencies, therefore add all libraries linked by
block-mount and blockd as direct dependencies to the corresponding
binary package definition.

This ensures that block-mount and blockd is automatically rebuilt and
relinked if any of these libraries has its ABI_VERSION updated in the
future.

Fixes: FS#2373
[jow: similar fix for procd and 98.42% of commit message]
Signed-off-by: Jo-Philip Wich <jow@mein.io>
Signed-off-by: Petr Štetiar <ynezz@true.cz>