arm64: make default NR_CPUS 8

Rather than continue to add per platform defaults, make the default a likely
common core count. 8 is also the default for x86.

Change-Id: Ifc6102acd021408cf341768bb9dbe104c4eca096
Signed-off-by: Rob Herring <rob.herring@calxeda.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Git-commit: 62aceb8ff4b3f442575eb7e23629da36020dca77
Git-Repo: git://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/


[rvaswani@codeaurora.org: resolve trivial merge conflicts]
Signed-off-by: Rohit Vaswani <rvaswani@codeaurora.org>