KVM: arm/arm64: Remove KVM_PRIVATE_MEM_SLOTS definition that are unused

arm/arm64 architecture doesnt use private memslots, hence removing
KVM_PRIVATE_MEM_SLOTS macro definition.

Reviewed-by: Christoffer Dall <cdall@linaro.org>
Signed-off-by: Linu Cherian <linu.cherian@cavium.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>