kconfig: Replace defconfig singe-symbol 'if's with 'depends on'

Same deal as in commit eddd98f ("kconfig: Replace some single-symbol
'if's with 'depends on'"), for all symbols defined within defconfig
files. See that commit for an explanation.

Maybe 'if's were used originally to mirror the 'if's in the main Kconfig
files, and then it got copied around by people assuming 'if' must work
differently from 'depends on'. It doesn't match in every spot at least.
Better to keep it simple and just consistently use 'depends on' when
it's a single symbol/choice I think. Helps reinforce that 'if' isn't
magic too.

Verified by printing all Kconfig menu nodes (symbols, choices, menus,
etc.) before and after the change and diffing (should show no
difference).

Signed-off-by: Ulf Magnusson <Ulf.Magnusson@nordicsemi.no>

boards/x86/acrn/Kconfig.defconfig

@@ -1,9 +1,6 @@
 # Copyright (c) 2019 Intel Corporation
 # SPDX-License-Identifier: Apache-2.0
 
-if BOARD_ACRN
-
 config BOARD
 	default "acrn"
-
-endif # BOARD_ACRN
+	depends on BOARD_ACRN

boards/x86/qemu_x86/Kconfig.defconfig

@@ -8,18 +8,12 @@ config BUILD_OUTPUT_BIN
 config BOARD
 	default "qemu_x86"
 
-if FLASH
-
 config FLASH_SIMULATOR
 	default y
-
-endif
+	depends on FLASH
 
 endif # BOARD_QEMU_X86
 
-if BOARD_QEMU_X86_64
-
 config BOARD
 	default "qemu_x86_64"
-
-endif # BOARD_QEMU_X86_64
+	depends on BOARD_QEMU_X86_64