arm: socfpga: imply/default common config options

This commit moves common config options used in all socfpga boards
to select/imply in Kconfig. This both cleans up the defconfig files
as well as makes future changes easier.

Options implied/defaulted for all sub-arches:
- SPL, SPL_DM, USE_TINY_PRINTF, NR_DRAM_BANKS

Options implied/defaulted for implied for A10 & gen5:
- FPGA_SOCFPGA, SYS_MALLOC_F_LEN, SYS_TEXT_BASE

Options implied/defaulted for gen5:
- SPL_STACK_R, SPL_SYS_MALLOC_SIMPLE, SPL_STACK_R_ADDR

Signed-off-by: Simon Goldschmidt <simon.k.r.goldschmidt@gmail.com>
Acked-by: Marek Vasut <marex@denx.de>