drm/panfrost: Add specific register offset macros for JS and MMU AS

Each Panfrost job has its own job slot and MMU address space set of
registers, which are selected with a job-specific index.

Turn the shift and stride used for selection of the right register set base
into a define rather than using magic numbers.

Signed-off-by: Adrián Larumbe <adrian.larumbe@collabora.com>
Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Signed-off-by: Steven Price <steven.price@arm.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220729144610.2105223-2-adrian.larumbe@collabora.com