soc/intel/common/cse: Add `cse_send_end_of_post()` as a public function

soc/intel/common/cse: Add `cse_send_end_of_post()` as a public function

This patch creates a global function `cse_send_end_of_post()` so
that IA common code may get access to this function for sending EOP
command to the HECI1/CSE device.

Additionally, use static variable to track and prevent sending EOP
command more than once in boot flow.

BUG=b:211954778
TEST=Able to build and boot Brya.

Signed-off-by: Subrata Banik <subratabanik@google.com>
Change-Id: I837c5723eca766d21b191b98e39eb52889498bfc
Reviewed-on: https://review.coreboot.org/c/coreboot/+/61519
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Lean Sheng Tan <sheng.tan@9elements.com>
Reviewed-by: EricR Lai <ericr_lai@compal.corp-partner.google.com>
Reviewed-by: Tim Wawrzynczak <twawrzynczak@chromium.org>
Reviewed-by: Maulik V Vaghela <maulik.v.vaghela@intel.com>