sparc64: implement global translation table entries v1

- match global tte against any context
- show global tte in MMU dump

v0->v1: added default case to switch statement in demap_tlb
- should fix gcc warning about uninitialized context variable

Signed-off-by: Igor V. Kovalenko <igor.v.kovalenko@gmail.com>
Signed-off-by: Blue Swirl <blauwirbel@gmail.com>
