efibootmgr(8): fix markup and style issues

[yuripv]

Summary

just something I noticed while actually reading the man page..

• fix markup in synopsis
• sort options
• fix issues reported by mandoc -Tlint

Test Plan

SYNOPSIS
     efibootmgr [-v]
     efibootmgr -a -b bootnum
     efibootmgr -A -b bootnum
     efibootmgr -B -b bootnum
     efibootmgr -c -l loader [-aD] [-b bootnum] [-k kernel] [-L label]
     efibootmgr -n -b bootnum
     efibootmgr -N
     efibootmgr -o bootorder
     efibootmgr -t timeout
     efibootmgr -T

[yuripv]

actually split the synopsis into separate options that can't be used together

[yuripv]

Warner, does this make sense to you/won't interfere with other changes you might be working on?

[imp]

This looks good to me.