sparc32: split ramdisk detection and reservation to a helper function

The detection and reservation of ramdisk memory were separated to allow
bootmem bitmap initialization after the ramdisk boundaries are detected.
Since the bootmem initialization is removed, the reservation of ramdisk
memory is done immediately after its boundaries are found.

Split the entire block into a separate helper function.

Signed-off-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Suggested-by: Sam Ravnborg <sam@ravnborg.org>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: David S. Miller <davem@davemloft.net>