arm64: dts: r8a7796: Add PWM device nodes

This patch adds PWM{0,1,2,3,4,5,6} device nodes for R8A7796 SoC.

Signed-off-by: Takeshi Kihara <takeshi.kihara.df@renesas.com>
[uli: added resets, shortened reg lengths to 8]
Signed-off-by: Ulrich Hecht <ulrich.hecht+renesas@gmail.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>