clk: bcm2835: Add bindings for the auxiliary peripheral clock gates.

These will be used for enabling UART1, SPI1, and SPI2.

Signed-off-by: Eric Anholt <eric@anholt.net>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Michael Turquette <mturquette@baylibre.com>