ARM: shmobile: r8a7778: cleanup registration of hspi

sh-hspi driver which doesn't need platform data at the time of
registration can be registerd on SoC.
And, registering these drivers in the SoC code can avoid
unwanted device numbering issue.
(ex. the hspi2 device number will be spi.0 if hspi2 only registered)
This patch registers it on SoC code as cleanup C code

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>