clk: bcm281xx: change some symbol names

As I developed the bcm281xx clock code I understood there were
restrictions on device tree "compatible" strings names, and as a
result "bcm11351" was used in places despite the part family being
more properly called "bcm281xx".  This can be a little confusing.

In some cases I went to far and things using "bcm11351" when that
was not necessary.

This patch remedies this.  It renames the symbol used to define the
"compatible" string (but not its value) so it uses "BCM281XX".
Similarly, the name names provided to the CLK_OF_DECLARE() macro
are changed, hoping to minimize the number of places that the
confusing "11351" string is used.

Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: Mike Turquette <mturquette@linaro.org>