Fix a 2038 bug.

If time_t is 64-bit (i.e. isn't 32-bit) allow any value of year not
just years less than 2038.

Don't both fixing the underflow in the case of years before 1903.
Add berirom(4), a device driver from the BERI hardware information ROM.
Build berirom(4) for BERI kernels and use it in place of altera_avgen(4)
to access this ROM.  Uses can now easily see the BERI CPU build time and
Subversion revision on the console.  For example:

berirom0: <BERI build information ROM> mem 0x7f00a000-0x7f00afff on simplebus0
berirom0: Built on 2014-04-28 at 12:04:58 (1398686698)
berirom0: SVN revision: r12398