soc/intel/common/pch: Decouple CLIENT from BASE

In preparation to add a third option, have "Client" platforms select a
dedicated Kconfig option instead of the common "_BASE" option. Rewrite
the help texts to clarify what "Client" and "Server" mean, because the
terms refer to the type of silicon and not to the market segment. Some
uniprocessor (single-socket) servers are actually client platforms and
there are some multi-socket workstations based on a server platform.

Change-Id: I646729d709f60ca2b5e74df18c2b4e52f9b10e6b
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/65951
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Sean Rhodes <sean@starlabs.systems>
Reviewed-by: Lean Sheng Tan <sheng.tan@9elements.com>

src/soc/intel/elkhartlake/Kconfig

@@ -56,7 +56,7 @@ config CPU_SPECIFIC_OPTIONS
 	select SOC_INTEL_COMMON_BLOCK_SMM
 	select SOC_INTEL_COMMON_BLOCK_SMM_IO_TRAP
 	select SOC_INTEL_COMMON_FSP_RESET
-	select SOC_INTEL_COMMON_PCH_BASE
+	select SOC_INTEL_COMMON_PCH_CLIENT
 	select SOC_INTEL_COMMON_RESET
 	select SOC_INTEL_MEM_MAPPED_PM_CONFIGURATION
 	select SSE2