modules: Only build sdhci_fdt for arm and arm64

Other FDT platform (like powerpc64* or riscv64) don't have gpio built
by default so just compile the module for those two arches.

Fixes: 9e08f82058cb ("modules: Add sdhci_fdt module")
(cherry picked from commit 0b426a1c2cef14ded10ded6ec737d5c116182996)