package/jamvm: restrict on what MIPS procs are allowed

package/jamvm: restrict on what MIPS procs are allowed

jamvm uses deprecated opcodes to store/load words from the FPU
coprocessor registers, and in so doing, expects those registers
to be 32-bit.

Thus, restrict the conditions under which jamvm is available
under mips.

Fixes:
    http://autobuild.buildroot.org/results/f76/f76e10e4c1ce25b42fb2e5d2012adf2eaf1b2fe1/
    http://autobuild.buildroot.org/results/162/162d0e41dc9bc6d6f6594ccee0cb4217067fc71f/
    ...

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>