efidev.4: Improve formatting.

• Move some information out of the SYNOPSIS section because it is formated in a broken way by mandoc(1) otherwise.
• Improve the formatting of the list of provided ioctls.
• Use "Fa" for struct fields.
• Pet mandoc and igor.
• Fix typos.

Reviewed by: kevans
Approved by: mat (mentor)
Differential Revision: https://reviews.freebsd.org/D16765