Initializes Mailbox in the same order of fields, and removes `mut` on configure_stage1.
Initializes Mailbox in the same order of fields, and removes `mut` on configure_stage1.

project-oak/hafnium-verification,project-oak/hafnium-verification,project-oak/hafnium-verification,project-oak/hafnium-verification,project-oak/hafnium-verification,project-oak/hafnium-verification,project-oak/hafnium-verification