If there is no register to save-restore or whitelist, just return. This
drops some noise from the log, particurlarly for platforms with several
engines like PVC:

	[drm:xe_reg_sr_apply_mmio [xe]] Applying bcs0 save-restore MMIOs
	[drm:xe_reg_sr_apply_whitelist [xe]] Whitelisting bcs0 registers
	[drm:xe_reg_sr_apply_mmio [xe]] Applying bcs1 save-restore MMIOs
	[drm:xe_reg_sr_apply_whitelist [xe]] Whitelisting bcs1 registers
	[drm:xe_reg_sr_apply_mmio [xe]] Applying bcs2 save-restore MMIOs
	[drm:xe_reg_sr_apply_whitelist [xe]] Whitelisting bcs2 registers
	[drm:xe_reg_sr_apply_mmio [xe]] Applying bcs5 save-restore MMIOs
	[drm:xe_reg_sr_apply_whitelist [xe]] Whitelisting bcs5 registers
	[drm:xe_reg_sr_apply_mmio [xe]] Applying bcs6 save-restore MMIOs
	[drm:xe_reg_sr_apply_whitelist [xe]] Whitelisting bcs6 registers
	[drm:xe_reg_sr_apply_mmio [xe]] Applying bcs7 save-restore MMIOs
	[drm:xe_reg_sr_apply_whitelist [xe]] Whitelisting bcs7 registers
	[drm:xe_reg_sr_apply_mmio [xe]] Applying bcs8 save-restore MMIOs
	[drm:xe_reg_sr_apply_whitelist [xe]] Whitelisting bcs8 registers
	[drm:xe_reg_sr_apply_mmio [xe]] Applying ccs0 save-restore MMIOs
	[drm:xe_reg_sr_apply_mmio [xe]] REG[0x20e4] = 0x00008000
	[drm:xe_reg_sr_apply_mmio [xe]] REG[0xb01c] = 0x00000001
	[drm:xe_reg_sr_apply_mmio [xe]] REG[0xe48c] = 0x00000800
	[drm:xe_reg_sr_apply_mmio [xe]] REG[0xe7c8] = 0x40000000
	...

On a PVC system it should show something like below. Whitelist calls
are still there since they aren't actually empty - driver just doesn't
print each individual entry. This will be fixed in future.

	[drm:xe_reg_sr_apply_whitelist [xe]] Whitelisting bcs0 registers
	[drm:xe_reg_sr_apply_whitelist [xe]] Whitelisting bcs1 registers
	[drm:xe_reg_sr_apply_whitelist [xe]] Whitelisting bcs2 registers
	[drm:xe_reg_sr_apply_whitelist [xe]] Whitelisting bcs5 registers
	[drm:xe_reg_sr_apply_whitelist [xe]] Whitelisting bcs6 registers
	[drm:xe_reg_sr_apply_whitelist [xe]] Whitelisting bcs7 registers
	[drm:xe_reg_sr_apply_whitelist [xe]] Whitelisting bcs8 registers
	[drm:xe_reg_sr_apply_mmio [xe]] Applying ccs0 save-restore MMIOs
	[drm:xe_reg_sr_apply_mmio [xe]] REG[0x20e4] = 0x00008000
	[drm:xe_reg_sr_apply_mmio [xe]] REG[0xb01c] = 0x00000001
	[drm:xe_reg_sr_apply_mmio [xe]] REG[0xe48c] = 0x00000800
	[drm:xe_reg_sr_apply_mmio [xe]] REG[0xe7c8] = 0x40000000

v2: Only tweak log verbosity, leave the whitelist printout for later
    since decoding the whitelist is more complex.
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://lore.kernel.org/r/20230314003012.2600353-3-lucas.demarchi@intel.comSigned-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>