drm/v3d: alloc and init job in one shot

Move job memory allocation to v3d_job_init function. This aim to facilitate
error handling in job initialization, since cleanup steps are similar for
all (struct v3d_job)-based types of job involved in a command submission.
To generalize v3d_job_init(), this change takes into account that all job
structs have the first element a struct v3d_job (bin, render, tfu, csd) or
it is a v3d_job itself (clean_job) for pointer casting.

v3:
- explicitly init job as NULL (Iago)
- fix pm failure handling on v3_job_init (Iago)

Suggested-by: Iago Toral Quiroga <itoral@igalia.com>
Signed-off-by: Melissa Wen <mwen@igalia.com>
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
Signed-off-by: Melissa Wen <melissa.srw@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/4d12e07bd334d2cddb51cabd359e99edde595619.1633016479.git.mwen@igalia.com