clk: sifive: avoid declaring static variables in includes

The existing code is unnecessarily convoluted:

Arrays __prci_init_clocks_fu[5|7]40  are initialized with data.
In separate includes fu[5|7]40-prci.h the size of the arrays is provided as
constants.

By moving the structures prci_clk_fu[5|7]40 to the respective code modules
we can directly use ARRAY_SIZE() to access the size of the data used for
initialization.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reviewed-by: Leo Yu-Chi Liang <ycliang@andestech.com>