powerpc: make kernel/nvram_64.c explicitly non-modular

The Makefile/Kconfig currently controlling compilation of this code is:

obj-$(CONFIG_PPC64)             += setup_64.o sys_ppc32.o \
                                   signal_64.o ptrace32.o \
                                   paca.o nvram_64.o firmware.o

arch/powerpc/platforms/Kconfig.cputype:config PPC64
arch/powerpc/platforms/Kconfig.cputype: bool "64-bit kernel"

...meaning that it currently is not being built as a module by anyone.

Lets remove the modular code that is essentially orphaned, so that
when reading the driver there is no doubt it is builtin-only.

Since module_init translates to device_initcall in the non-modular
case, the init ordering remains unchanged with this commit.

We don't replace module.h with init.h since the file already has that.

We delete the MODULE_LICENSE tag since that information is already
contained at the top of the file in the comments.

Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Hari Bathini <hbathini@linux.vnet.ibm.com>
Cc: Nathan Fontenot <nfont@linux.vnet.ibm.com>
Cc: Andrzej Hajda <a.hajda@samsung.com>
Cc: Anton Blanchard <anton@samba.org>
Cc: linuxppc-dev@lists.ozlabs.org
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Reviewed-by: Nathan Fontenot <nfont@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>