T8085: Do not hardcode values in kernel build scripts

[asklymenko]

Change summary

Add architecture detection for kernel configuration file to replace the hardcoded value.

We can't specify it with the following one line:
KERNEL_CONFIG=arch/${ARCH}/configs/vyos_defconfig

It is caused by the current directory structure - amd64 config is stored in linux/arch/x86 directory in the kernel sources. That's why we have to specify every option separately. Both uname and dpkg utils return this value in format of "x86_64" or "armd64" strings.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Code style update (formatting, renaming)
• Refactoring (no functional changes)
• Migration from an old Vyatta component to vyos-1x, please link to related PR inside obsoleted component
• Other (please describe):

Related Task(s)

• https://vyos.dev/T8085

Related PR(s)

Checklist:

• I have read the CONTRIBUTING document
• I have linked this PR to one or more Phabricator Task(s)
• My commit headlines contain a valid Task id
• My change requires a change to the documentation
• I have updated the documentation accordingly

[github-actions]

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No issues in PR Title / Commit Title

[sever-sever]

Fix for the build kernel architecture.
The x86 was hardcoded in the build kernel script.
Fix it.

[c-po]

De-hardcode Kernel config path