loader: Use tslog to instrument some functions

In my initial testing, these are the functions which showed up as
being worth instrumenting. More may be added later.

common/console.c: cons_probe
common/gfx_fb.c: read_list, insert_font, autoload_font
common/interp.c: interact
common/interp_lua.c: interp_init, interp_run
efi/libefi/efipart.c: efipart_readwrite
i386/libi386/biosdisk.c: bd_init, bd_open, bd_edd_io, bd_chs_io, bd_io
libsa/open.c: open
libsa/read.c: read
libsa/twiddle.c: twiddle

Note that profiling interp_run may be of questionable utility as it
may depend on user behaviour (e.g. pressing keys).

Reviewed by: kevans (earlier version)