drm/i915: Extend rpm wakelock for debugfs/i915_drpc_info

drm/i915: Extend rpm wakelock for debugfs/i915_drpc_info

i915_drpc_info missed covering a few register read with the runtime pm
wakelock. Be simple and cover the entire function with a single wakelock
so that new additions are not similarly missed in future.

  WARNING: CPU: 2 PID: 1334 at drivers/gpu/drm/i915/intel_drv.h:1743 gen6_read32+0x192/0x1e0 [i915]
  RPM wakelock ref not held during HW access
  Modules linked in: rpcsec_gss_krb5 nfsv4 dns_resolver netconsole nfsd auth_rpcgss ipmi_watchdog ipmi_poweroff ipmi_devintf ipmi_msghandler overlay btrfs xor raid6_pq dm_mod sg sd_mod snd_hda_codec_hdmi snd_hda_codec_realtek snd_hda_codec_generic ata_generic pata_acpi intel_rapl x86_pkg_temp_thermal intel_powerclamp coretemp snd_hda_intel kvm_intel snd_hda_codec kvm eeepc_wmi irqbypass snd_hda_core crct10dif_pclmul crc32_pclmul crc32c_intel asus_wmi sparse_keymap ghash_clmulni_intel snd_hwdep i915 rfkill ppdev pcbc aesni_intel ata_piix crypto_simd glue_helper snd_pcm pata_via cryptd pcspkr snd_timer drm_kms_helper syscopyarea snd sysfillrect libata sysimgblt fb_sys_fops soundcore shpchp drm wmi parport_pc parport tpm_infineon video
  CPU: 2 PID: 1334 Comm: php5 Not tainted 4.10.0-rc8-01615-g1f58c8e #1
  Hardware name: System manufacturer System Product Name/P8H67-M PRO, BIOS 1002 04/01/2011
  Call Trace:
   dump_stack+0x63/0x8a
   __warn+0xcb/0xf0
   warn_slowpath_fmt+0x4f/0x60
   ? seq_vprintf+0x35/0x50
   gen6_read32+0x192/0x1e0 [i915]
   i915_drpc_info+0x55d/0x990 [i915]
   seq_read+0xf2/0x3b0
   full_proxy_read+0x51/0x80
   __vfs_read+0x28/0x130
   ? security_file_permission+0x9b/0xc0
   ? rw_verify_area+0x4e/0xb0
   vfs_read+0xa8/0x170
   SyS_read+0x46/0xa0
   entry_SYSCALL_64_fastpath+0x1a/0xa9
  RIP: 0033:0x7fd97bf175a0
  RSP: 002b:00007ffdf730db68 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
  RAX: ffffffffffffffda RBX: 00007fd978028738 RCX: 00007fd97bf175a0
  RDX: 0000000000002000 RSI: 00007fd97740e0d8 RDI: 0000000000000005
  RBP: 0000000000000001 R08: 0000000000e97840 R09: 00007fd977ef8d58
  R10: 0000000000000027 R11: 0000000000000246 R12: 00007fd977ef8d58
  R13: 0000000000000000 R14: 0000000000eb4640 R15: 0000000000000000

Reported-by: kernel test robot <xiaolong.ye@intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/20170313095617.29010-1-chris@chris-wilson.co.uk
Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com>