drm/i915: do not pass dev_priv to low-level forcewake functions

The only usage we have for it is for the regs pointer. Save a pointer to
the set and ack registers instead of the register offsets to remove this
requirement

v2: Keep passing uncore down to the lowest levels to avoid repeated
pointer chasing in the innermost loops:

add/remove: 0/0 grow/shrink: 3/15 up/down: 33/-155 (-122)
Function                                     old     new   delta
fw_domain_init                               320     351     +31
hdmi_port_clock_valid                        319     320      +1
g4x_pre_enable_dp                            364     365      +1
ring_request_alloc                          1852    1851      -1
intel_engine_lookup_user                      50      49      -1
gen11_irq_handler                            738     737      -1
__intel_uncore_forcewake_get                 115     112      -3
intel_uncore_fw_release_timer                198     194      -4
i915_forcewake_domains                       154     150      -4
fw_domain_fini                               172     168      -4
__intel_uncore_forcewake_put                 163     159      -4
___force_wake_auto                           138     134      -4
fw_domains_put                                98      92      -6
__err_print_to_sgl                          4058    4052      -6
intel_uncore_forcewake_reset                 459     444     -15
fw_domains_get                               563     548     -15
fw_domain_wait_ack_with_fallback             490     450     -40
fw_domains_get_with_fallback                 875     828     -47

Cc: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20190313231319.711-2-daniele.ceraolospurio@intel.com
Link: https://patchwork.freedesktop.org/patch/msgid/20190316100045.20240-1-chris@chris-wilson.co.uk