Closed issue by dawidpotocki on void-packages repository

https://github.com/void-linux/void-packages/issues/18612

Description:
### System

* xuname:
  `Void 5.4.15_1 x86_64 GenuineIntel notuptodate rFFF`
* package:
  `fwupd-1.3.6_1`

### Expected behavior

fwupd is able to update firmware, efivars are mounted.

### Actual behavior

When I'm doing `$ fwupdmgr get-devices`, I get
`Update Error:        /sys/firmware/efi/efivars was not mounted`
Then when I try updating with `# fwupdmgr update`, I get
```
No upgrades for System Firmware: is not updatable
No upgrades for UEFI Device Firmware: is not updatable
No upgrades for UEFI Device Firmware: is not updatable
```

### Fix

The problem is that efivars are not mounted by Void. Doing something like this
will fix this issue.

```
$ sudo mount -t efivarfs efivarfs /sys/firmware/efi/efivars
```

After this, it should work just fine

```
$ sudo fwupdmgr get-updates
$ fwupdmgr get-devices
```

efivars have to be mounted as RW, not RO.
Since `/sys/firmware/efi/efivars` isn't immutable prior to kernel 4.5, doing
something like `rm -rf` on it can brick the device.

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=ed8b0de5a33d2a2557dce7f9429dca8cb5bc5879

### Steps to reproduce the behavior

1. Install `fwupd`
2. Run `fwupdmgr get-devices`
3. Run `fwupdmgr update` as root