makefiles: add missing dependencies on DEV_SYSROOT_INIT_STAMP

Reviewed By: curt
Testing Done: make -j32 all

dmidecode.make and gptfdisk.make were missing dependencies on the development
sysroot.  This causes a build error for distclean trees.

Add the dependencies, fix the build error.

I also modified i2ctools.make to use the same order-only-prerequisite the other
targets use.

Signed-off-by: Dustin Byford <dustin@cumulusnetworks.com>