riscv: Call identify_cpu() earlier for CPU 0

It is advantageous to have knowledge of ISA features as early as
possible. For example, the presence of newer virtual memory extensions
may be useful to pmap_bootstrap().

To achieve this, split out the printf() parts of identify_cpu() into a
separate function, printcpuinfo(). This latter function will be called
later in boot after the console has been initialized.

Reviewed by: markj
MFC after: 2 weeks
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D39810