Cleaned up ELF64 address handling.

* platform_allocate_elf_region() is removed, it is implemented in platform-
  independent code now (ELF*Class::AllocateRegion). For ELF64 it is now
  assumed that 64-bit addresses are mapped in the loader's 32-bit address space
  as (address - KERNEL_BASE_64BIT + KERNEL_BASE).
* mapped_delta field from preloaded_*_image removed, now handled compile-time
  using the ELF*Class::Map method.
* Also link the kernel with -z max-page-size=0x1000, removes the need for
  2MB alignment on the data segment (not going to map the kernel with large
  pages for the time being).

build/jam/BuildSetup

@@ -388,6 +388,7 @@ switch $(HAIKU_ARCH) {
 		# code due to interrupts.
 		HAIKU_KERNEL_CCFLAGS += -mcmodel=kernel -mno-red-zone ;
 		HAIKU_KERNEL_C++FLAGS += -mcmodel=kernel -mno-red-zone ;
+		HAIKU_KERNEL_PIC_LINKFLAGS += -z max-page-size=0x1000 ;
 
 		# Bootloader is 32-bit.
 		HAIKU_BOOT_LINKFLAGS += -m elf_i386_haiku ;