kernel/arch/sparc: stubs to get the kernel to link

Add empty implementation of timer, elf, vm, debugger support, to let the
kernel link.

Also add the kernel linker script.

Change-Id: If0795fa6554aea3df1ee544c25cc4832634ffd78
Reviewed-on: https://review.haiku-os.org/c/1108
Reviewed-by: waddlesplash <waddlesplash@gmail.com>