meson: make target endianneess available to Kconfig

Some targets use "default y" for boards to filter out those that require
TCG.  For consistency we are switching all other targets to do the same.
MIPS boards may only be available for big-endian or only for
little-endian emulators, add a symbol so that this can be described
with a "depends on" clause.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2 files changed