clk: bcm2835: Move under bcm/ with other Broadcom SoC clk drivers.

clk-bcm2835.c predates the drivers under bcm/, but all the new BCM
drivers are going in there so let's follow them.

Signed-off-by: Eric Anholt <eric@anholt.net>
Acked-by: Stephen Warren <swarren@wwwdotorg.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>