[ISSUE] Support intel-ucode when using mkinitcpio

[basploeger <basploeger@users.noreply.github.com>]

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New issue by basploeger on void-packages repository

https://github.com/void-linux/void-packages/issues/48145

Description:
### Is this a new report?

Yes

### System Info

Void 6.6.10_1 x86_64 GenuineIntel uptodate rrrmFFFFFF

### Package(s) Affected

intel-ucode-20231114_1, mkinitcpio-37_3

### Does a report exist for this bug with the project's home (upstream) and/or another distro?

No. But [this information](https://wiki.archlinux.org/title/microcode#Initrd_images) from Arch Linux is useful for reference.

Arch's intel-ucode package generates the necessary `/boot/intel-ucode.img` [here](https://gitlab.archlinux.org/archlinux/packaging/packages/intel-ucode/-/blob/main/PKGBUILD?ref_type=heads#L22). 

### Expected behaviour

Intel microcode gets loaded in early boot before loading the initramfs produced by mkinitcpio.

### Actual behaviour

Intel microcode does not get loaded as testified by the following console error messages before initramfs gets loaded:

```
TSC_DEADLINE disabled due to Errata; please update microcode to version: 0x52 (or later)
RETBleed: WARNING: Spectre v2 mitigation leaves CPU vulnerable to RETBleed attacks, data leaks possible!
```

These error messages disappear when loading an initramfs produced by dracut, as the intel-ucode package supports dracut already.

### Steps to reproduce

1. Install intel-ucode.
2. [Switch](https://docs.voidlinux.org/config/kernel.html#changing-the-default-initramfs-generator) from dracut to mkinitcpio
3. Reboot