package/grantlee: disable for nios2 and microblaze

Disable grantlee due to a toolchain issue on nios2 and microblaze architecture [1].
Issue reproduced with binutils 2.26 and GCC 6

Fixes (microblaze):
http://autobuild.buildroot.net/results/091/091bf7df46d6057be44b8ca8653596bd84c38fbc

Fixes (nios2):
http://autobuild.buildroot.net/results/e05/e05280f1cc4f669b7e418161749290723179e987

[1] https://sourceware.org/bugzilla/show_bug.cgi?id=20173



Signed-off-by: Romain Naour <romain.naour@gmail.com>
[Thomas:
 - tweak how the dependency is expressed
 - propagate the dependency to the comments.]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>