platform/x86: intel_telemetry_debugfs: fix oops when load/unload module

This fixes an oops found while testing load/unload of the
intel_telemetry_debugfs module. module_init uses register_pm_notifier
for PM callbacks, but unregister_pm_notifier was missing from
module_exit.

 [ 97.481860] BUG: unable to handle kernel paging request at ffffffffa006f010
 [ 97.489742] IP: blocking_notifier_chain_register+0x3a/0xa0
 [ 97.495898] PGD 2e0a067
 [ 97.495899] PUD 2e0b063
 [ 97.498737] PMD 179e29067
 [ 97.501573] PTE 0

 [ 97.508423] Oops: 0000 1 PREEMPT SMP
 [ 97.512724] Modules linked in: intel_telemetry_debugfs intel_rapl gpio_keys dwc3 udc_core intel_telemetry_pltdrv intel_punit_ipc intel_telemetry_core rtc_cmos efivars x86_pkg_temp_thermal iwlwifi snd_hda_codec_hdmi soc_button_array btusb cfg80211 btrtl mei_me hci_uart btbcm mei btintel i915 bluetooth intel_pmc_ipc snd_hda_intel spi_pxa2xx_platform snd_hda_codec dwc3_pci snd_hda_core tpm_tis tpm_tis_core tpm efivarfs
 [ 97.558453] CPU: 0 PID: 889 Comm: modprobe Not tainted 4.11.0-rc6-intel-dev-bkc #1
 [ 97.566950] Hardware name: Intel Corp. Joule DVT3/SDS, BIOS GTPP181A.X64.0143.B30.1701132137 01/13/2017
 [ 97.577518] task: ffff8801793a21c0 task.stack: ffff8801793f0000
 [ 97.584162] RIP: 0010:blocking_notifier_chain_register+0x3a/0xa0
 [ 97.590903] RSP: 0018:ffff8801793f3c58 EFLAGS: 00010286
 [ 97.596802] RAX: ffffffffa006f000 RBX: ffffffff81e3ea20 RCX: 0000000000000000
 [ 97.604812] RDX: ffff880179eaf210 RSI: ffffffffa0131000 RDI: ffffffff81e3ea20
 [ 97.612821] RBP: ffff8801793f3c68 R08: 0000000000000006 R09: 000000000000005c
 [ 97.620847] R10: 0000000000000000 R11: 0000000000000006 R12: ffffffffa0131000
 [ 97.628855] R13: 0000000000000000 R14: ffff880176e35f48 R15: ffff8801793f3ea8
 [ 97.636865] FS: 00007f7eeba07700(0000) GS:ffff88017fc00000(0000) knlGS:0000000000000000
 [ 97.645948] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
 [ 97.652423] CR2: ffffffffa006f010 CR3: 00000001775ef000 CR4: 00000000003406f0
 [ 97.660423] Call Trace:
 [ 97.663166] ? 0xffffffffa0031000
 [ 97.666885] register_pm_notifier+0x18/0x20
 [ 97.671581] telemetry_debugfs_init+0x92/0x1000

Signed-off-by: Priyalee Kushwaha <priyalee.kushwaha@intel.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Darren Hart (VMware) <dvhart@infradead.org>