sparc: Fix /proc/kcore

/proc/kcore investigates the "System RAM" elements in /proc/iomem to
initialize it's memory tables.  Therefore we have to register them
before it tries to do so.  kcore uses device_initcall() so let's
use arch_initcall() for the registry.

Also we need ARCH_PROC_KCORE_TEXT to get the virtual addresses of
the kernel image correct.

Reported-by: David Ahern <david.ahern@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>