ARM: shmobile: timer: r8a73a4 and r8a7790 are multi-platform only

Since commits e0426818 ("ARM: shmobile: r8a7790: Remove legacy
code") and 9d07d414 ("ARM: shmobile: r8a73a4: ape6evm: Remove
legacy platform"), the R-Mobile APE6 and R-Car H2 SoCs are supported by
multiplatform kernels only.
Hence we can drop checks for these SoCs in legacy kernel builds.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>