ARM: shmobile: r8a73a4: Rename cmt registration helper

Rename r8a7790_register_cmt() as r8a73a4_register_cmt() to
reflect name of the SoC in use. The use of r8a7790 appears
to be due to historical sharing of code from that SoC.
Shared code is no longer used.

Signed-off-by: Simon Horman <horms+renesas@verge.net.au>