soc/intel/elkhartlake: Fix EHL mainboard build fail errors

When EHL initial mainboard patch is uploaded, there are some build
errors caused by EHL soc codes. Here are the fixes:
1. include gpio_op.asl to resolve undefined variables in scs.asl
2. remove unused variables in fsp_params.c
3. rearrage sequences of #includes to fix build dependency of
   soc/gpio_defs.h in intelblocks/gpio.h
4. add the __weak to mainboard_memory_init_params function
5. add the missing _len as per this patch changes
   https://review.coreboot.org/c/coreboot/+/45873

Signed-off-by: Tan, Lean Sheng <lean.sheng.tan@intel.com>
Change-Id: Idaa8b0b5301742287665abde065ad72965bc62b3
---
M src/soc/intel/elkhartlake/acpi/gpio.asl
M src/soc/intel/elkhartlake/fsp_params.c
M src/soc/intel/elkhartlake/include/soc/gpio.h
M src/soc/intel/elkhartlake/romstage/fsp_params.c
M src/soc/intel/elkhartlake/romstage/romstage.c
5 files changed, 4 insertions(+), 7 deletions(-)