clk: sprd: Select REGMAP_MMIO to avoid compile errors

[ Upstream commit c9a67cbb5189e966c70451562b2ca4c3876ab546 ]

Make REGMAP_MMIO selected to avoid undefined reference to regmap symbols.

Fixes: d41f59fd ("clk: sprd: Add common infrastructure")
Signed-off-by: Chunyan Zhang <chunyan.zhang@unisoc.com>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>