ARM: shmobile: r8a7740: add SoC clocks to DTS

Declares the r8a7740 clocks supported by the legacy clock framework,
excluding those requiring extensions to the DIV6 driver.

Signed-off-by: Ulrich Hecht <ulrich.hecht+renesas@gmail.com>
Acked-by: Magnus Damm <damm+renesas@opensource.se>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>