soc: intel_adsp: ace: Clean up macro indentation in power_down.S

This commit improves the readability of the power_down.S assembly file
by standardizing the indentation of the preprocessor definitions.

No functional changes have been made; this is purely a cosmetic update
to the code formatting.

Signed-off-by: Tomasz Leman <tomasz.m.leman@intel.com>