arm64: mm: use ubfm for dcache_line_size

Use 'ubfm' for the bitfield move instruction; thus, single
instruction can be used instead of two instructions, when
getting the minimum D-cache line size from CTR_EL0 register.

Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>