tree: Drop Intel Ice Lake support

Intel Ice Lake is unmaintained and the only user of this platform ever
was the Intel CRB (Customer Reference Board). As it looks like, it was
never ready for production as only engineering sample CPUIDs are
supported.

As announced in the 4.19 release notes, remove support for Intel
Icelake code and move any maintenance on the 4.19 branch.

This affects the following components and their related code:

  * Intel Ice Lake SoC
  * Intel Ice Lake CRB mainboard
  * Documentation

Change-Id: Ia796d4dc217bbcc3bbd9522809ccff5a46938094
Signed-off-by: Felix Singer <felixsinger@posteo.net>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/72008
Reviewed-by: Subrata Banik <subratabanik@google.com>
Reviewed-by: Elyes Haouas <ehaouas@noos.fr>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/include/cpu/intel/cpu_ids.h

@@ -36,8 +36,6 @@
 #define CPUID_COFFEELAKE_B0		0x906eb
 #define CPUID_COFFEELAKE_P0		0x906ec
 #define CPUID_COFFEELAKE_R0		0x906ed
-#define CPUID_ICELAKE_A0		0x706e0
-#define CPUID_ICELAKE_B0		0x706e1
 #define CPUID_JASPERLAKE_A0		0x906c0
 #define CPUID_COMETLAKE_U_A0		0xa0660
 #define CPUID_COMETLAKE_U_K0_S0		0xa0661