Instead of storing the current Processor into a core local register, we
currently just store it into a global, since we don't support SMP for
aarch64 anyway. This simplifies the initial implementation.
Since kmalloc() now works, we can actually load the kernel symbol table!
This in turn allows us to call dump_backtrace(), and actually get a
useful backtrace in the aarch64 Kernel.
As there is no need for a Prekernel on aarch64, the Prekernel code was
moved into Kernel itself. The functionality remains the same.
SERENITY_KERNEL_AND_INITRD in run.sh specifies a kernel and an inital
ramdisk to be used by the emulator. This is needed because aarch64
does not need a Prekernel and the other ones do.