drm/imagination: Access FW initialised state with READ/WRITE_ONCE

drm/imagination: Access FW initialised state with READ/WRITE_ONCE

Update FW initialised state shared resource access with READ/WRITE_ONCE
to prevent following:
- Non-atomic access to variable in multi-thread/CPU case.
- Merge successive loads from the same variable.

Signed-off-by: Brajesh Gupta <brajesh.gupta@imgtec.com>
Reviewed-by: Matt Coster <matt.coster@imgtec.com>
Link: https://patch.msgid.link/20260519-b4-context_reset-v2-4-931018a7131d@imgtec.com
Signed-off-by: Matt Coster <matt.coster@imgtec.com>