Kconfig: Remove EXPERT mode

After much consideration, and many years of an EXPERT mode sitting
almost completely unused, we've seen that it doesn't work for us.
There is no standard on what constitutes EXPERT, and most of
coreboot's options Kconfig are expert-level.

We even joked that not selecting "EXPERT" should prevent coreboot
from compiling:

@echo $(shell whoami) is not permitted to compile coreboot

Change-Id: Ic22dd54a48190b81d711625efb6b9f3078f41778
Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
Reviewed-on: http://review.coreboot.org/11365
Tested-by: build bot (Jenkins)
Reviewed-by: Alexander Couzens <lynxis@fe80.eu>

payloads/external/SeaBIOS/Kconfig

@@ -18,7 +18,6 @@ endchoice
 config SEABIOS_PS2_TIMEOUT
 	prompt "PS/2 keyboard controller initialization timeout (milliseconds)"
 	default 0
-	depends on EXPERT
 	int
 	help
 	  Some PS/2 keyboard controllers don't respond to commands immediately