package/jemalloc: filter on suported architectures

jemalloc has a hard-coded list of supported architectures, which it uses
to define the minimum alignment for allocations. It whines at build time
(not at configure time) when it does not know that alignment.

Fix that by making jemalloc depend on the known-supported architectures.

Fixes:
    http://autobuild.buildroot.org/results/674/674b6022f9a403528a758c0785656d2bda79e0a9/



Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Eric Le Bihan <eric.le.bihan.dev@free.fr>
Reviewed-by: Romain Naour <romain.naour@gmail.com>
[Thomas:
 - split ARM and AArch64 dependencies on two lines
 - for SuperH, instead of using BR2_sh && !BR2_sh2, explicitly list the
   SH4 variants, since only SH4 is supported by jemalloc.]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>