soc/intel/skylake: Enable compression on FSP-S

Use LZ4 algorithm to compress FSP-S. This saves ~40 KiB and reduces the
boot time by ~7 ms. LZMA would save a further ~1 KiB, but adds ~9 ms to
the boot time.

LZMA size:
fsps_lzma.bin	0xb0dc0    fsp	146578 LZMA (188416 decompressed)
LZMA decompression time:
  15:starting LZMA decompress (ignore for x86)         388,716 (47,646)
  16:finished LZMA decompress (ignore for x86)         406,167 (17,450)

LZ4 size:
fsps_lz4.bin	0x242dc0   fsp	147442 LZ4  (188416 decompressed)
LZ4 decompression time:
  17:starting LZ4 decompress (ignore for x86)          384,736 (47,864)
  18:finished LZ4 decompress (ignore for x86)          384,796 (59)

Change-Id: Idace01227cfd2312b2c4c4ea1e6aaac8c21cd6b0
Signed-off-by: Benjamin Doron <benjamin.doron00@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/50726
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Furquan Shaikh <furquan@google.com>
Reviewed-by: Karthik Ramasubramanian <kramasub@google.com>

src/soc/intel/skylake/Kconfig

@@ -25,6 +25,7 @@ config CPU_SPECIFIC_OPTIONS
 	select CPU_INTEL_COMMON
 	select CPU_INTEL_FIRMWARE_INTERFACE_TABLE
 	select CPU_SUPPORTS_PM_TIMER_EMULATION
+	select FSP_COMPRESS_FSP_S_LZ4
 	select FSP_M_XIP
 	select FSP_STATUS_GLOBAL_RESET_REQUIRED_3
 	select GENERIC_GPIO_LIB