drm/panthor: Support 64-bit endpoint_req register for Mali-G1

drm/panthor: Support 64-bit endpoint_req register for Mali-G1

Add support for the 64-bit endpoint_req register introduced in CSF v4.0+
GPUs. Unlike a simple register widening, the 64-bit variant occupies the
next 64 bits after the original 32-bit field, requiring
version-dependent access.

This change introduces helper functions to read, write, and update the
endpoint_req register, ensuring correct handling on both pre-v4.0 and
v4.0+ firmwares.

Reviewed-by: Steven Price <steven.price@arm.com>
Signed-off-by: Karunika Choo <karunika.choo@arm.com>
Link: https://patch.msgid.link/20251125125548.3282320-8-karunika.choo@arm.com
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>