Revert "Kconfig: Bring HEAP_SIZE to a common, large value"

This reverts commit 44a48ce7a4.

Reason for revert: It breaks wakeup from suspend on a bunch of boards.

While this approach of eyeballing "correct" values by chipset _should_
be fixed, it should also be accompanied by compile time verification
that the memory map works out.

Since nobody seems to care enough, let's just revert this, instead of
keeping the tree broken for a bunch of configurations.

Change-Id: I3cd73b6ce8b15f06d3480a03ab472dcd444d7ccc
Signed-off-by: Patrick Georgi <patrick@coreboot.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/78850
Reviewed-by: Matt DeVillier <matt.devillier@amd.corp-partner.google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Martin L Roth <gaumless@gmail.com>
Reviewed-by: Nico Huber <nico.h@gmx.de>
Reviewed-by: Subrata Banik <subratabanik@google.com>

src/Kconfig

@@ -751,7 +751,8 @@ config RTC
 
 config HEAP_SIZE
 	hex
-	default 0x100000
+	default 0x100000 if FLATTENED_DEVICE_TREE
+	default 0x4000
 
 config STACK_SIZE
 	hex