sparc: add kernel debug output

Mostly the same as PowerPC, using OpenFirmware.

Change-Id: I197cc181e92da92c272ee9cfa20c8ad2d2c63d41
Reviewed-on: https://review.haiku-os.org/c/haiku/+/3579
Reviewed-by: waddlesplash <waddlesplash@gmail.com>

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>