hal/ia32: Rename dr4 and dr5 to dr6 and dr7

[astalke]

Description

Debug registers DR4 and DR5 are reserved when debug extensions are
enabled (when the DE flag in control register CR4 is set) and attempts
to reference the DR4 and DR5 registers cause invalid-opcode exceptions
(#UD). When debug extensions are not enabled (the DE flag is clear),
these registers are aliased to debug registers DR6 and DR7

JIRA: RTOS-307

Motivation and Context

The change is required for the system to work on some hardware.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

How Has This Been Tested?

• Already covered by automatic testing.
• New test added: (add PR link here).
• Tested by hand on: ia32-generic-pc

Checklist:

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing linter checks and tests passed.
• My changes generate no new compilation warnings for any of the targets.

Special treatment

• This PR needs additional PRs to work (list the PRs, preferably in merge-order).
• I will merge this PR by myself when appropriate.

[gerard5]

Add to commit message the following e.g.:
Debug registers DR4 and DR5 are reserved when debug extensions are
enabled (when the DE flag in control register CR4 is set) and attempts
to reference the DR4 and DR5 registers cause invalid-opcode exceptions
(#UD). When debug extensions are not enabled (the DE flag is clear),
these registers are aliased to debug registers DR6 and DR7

Or even better as comment in the code, in exceptions.h (may be short as in the PR description).

[astalke]

Add to commit message the following e.g.: Debug registers DR4 and DR5 are reserved when debug extensions are enabled (when the DE flag in control register CR4 is set) and attempts to reference the DR4 and DR5 registers cause invalid-opcode exceptions (#UD). When debug extensions are not enabled (the DE flag is clear), these registers are aliased to debug registers DR6 and DR7

Or even better as comment in the code, in exceptions.h

Done

[gerard5]

Looks good to me.