tslog: Annotate some early boot functions

Booting an amd64 kernel on Firecracker with 1 CPU and 128 MB of RAM,
hammer_time takes roughly 2740 us:

• 55 us in xen_pvh_parse_preload_data
  • 20 us in boot_parse_cmdline_delim
  • 20 us in boot_env_to_howto
• 15 us in identify_hypervisor
• 1320 us in link_elf_reloc
  • 1310 us in relocate_file1 handling ef->rela
• 25 us in init_param1
• 30 us in dpcpu_init
• 355 us in initializecpu
  • 255 us in initializecpu calling load_cr4
• 425 us in getmemsize
  • 280 us in pmap_bootstrap
    • 205 us in create_pagetables
• 10 us in init_param2
• 25 us in pci_early_quirks
• 60 us in cninit
• 90 us in kdb_init
• 105 us in msgbufinit
• 20 us in fpuinit
• 205 us elsewhere in hammer_time

Some of these are unavoidable (e.g. identify_hypervisor uses CPUID and
load_cr4 loads the CR4 register, both of which trap to the hypervisor)
but others may deserve attention.

Sponsored by: https://www.patreon.com/cperciva
Differential Revision: https://reviews.freebsd.org/D40325