soc/intel/alderlake: Increase premem cbmem buffer size to 16KB

Current size of the cbmem premem buffer (8KB) is sometimes insufficient
to contain the complete debug log causing the cbmem console buffer to
indicate overflow.

This patch increases the premem cbmem buffer size to 16KB so that
the complete debug log can be stored in it.

TEST=Make sure that logs from all the boot stages can be seen using
'cbmem -c'.

Change-Id: I60c68322c52191eabf7e06b4be06e66f90ff8751
Signed-off-by: Tarun Tuli <taruntuli@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/71290
Reviewed-by: Subrata Banik <subratabanik@google.com>
Reviewed-by: Kapil Porwal <kapilporwal@google.com>
Reviewed-by: Nick Vaccaro <nvaccaro@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/soc/intel/alderlake/Kconfig

@@ -382,7 +382,7 @@ config CBFS_SIZE
 config PRERAM_CBMEM_CONSOLE_SIZE
 	hex
 	default 0x16000 if CONSOLE_SERIAL
-	default 0x2000
+	default 0x4000
 
 config CONSOLE_CBMEM_BUFFER_SIZE
 	hex