arm64: mm: remove unused functions and variable protoypes

The functions __cpu_flush_user_tlb_range and __cpu_flush_kern_tlb_range
were removed in commit fa48e6f780 'arm64: mm: Optimise tlb flush logic
where we have >4K granule'. Global variable cpu_tlb was never used in
arm64.

Remove them.

Signed-off-by: Yingjoe Chen <yingjoe.chen@mediatek.com>
Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

diff --cc arch/arm64/include/asm/tlbflush.h
Simple merge