Reverse keymap search order

[fauxpark]

Description

If a keyboard has two keymaps with the same name at multiple levels (eg. keyboardname and keyboardname/rev3 where rev1 and rev2 can share a keymap, but rev3 differs), the makefile logic will pick up the highest-level keymap instead.

Types of Changes

• Core
• Bugfix
• New feature
• Enhancement/optimization
• Keyboard (addition or update)
• Keymap/layout/userspace (addition or update)
• Documentation

Issues Fixed or Closed by This PR

Checklist

• My code follows the code style of this project: C, Python
• I have read the PR Checklist document and have made the appropriate changes.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• I have tested the changes and verified that they work and don't break anything (as well as I can manage).

[fauxpark]

CI failure is expected; the affected boards will need a followup PR to fix the layouts.

[drashna]

wait, would this prefer the board/rev3 or board keymap?

[fauxpark]

The former. Note CI here is passing where dimple rev3 and infinity87 are failing in current develop builder.

[zvecr]

Do we want such a logic change to go to master rather than develop?

[fauxpark]

May as well, I'm pretty confident the two boards above are the only ones affected, but just in case...