Convert CONFIG_ENV_IS_IN_FLASH to Kconfig

This converts the following to Kconfig:
   CONFIG_ENV_IS_IN_FLASH

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/powerpc/cpu/mpc83xx/Kconfig b/arch/powerpc/cpu/mpc83xx/Kconfig
index cdd21a2..b5b26f9 100644
--- a/arch/powerpc/cpu/mpc83xx/Kconfig
+++ b/arch/powerpc/cpu/mpc83xx/Kconfig
@@ -13,6 +13,7 @@
 
 config TARGET_SBC8349
 	bool "Support sbc8349"
+	imply ENV_IS_IN_FLASH
 
 config TARGET_VE8313
 	bool "Support ve8313"
@@ -39,6 +40,7 @@
 config TARGET_MPC832XEMDS
 	bool "Support MPC832XEMDS"
 	select BOARD_EARLY_INIT_F
+	imply ENV_IS_IN_FLASH
 
 config TARGET_MPC8349EMDS
 	bool "Support MPC8349EMDS"
@@ -50,6 +52,7 @@
 config TARGET_MPC8349ITX
 	bool "Support MPC8349ITX"
 	imply CMD_IRQ
+	imply ENV_IS_IN_FLASH
 
 config TARGET_MPC837XEMDS
 	bool "Support MPC837XEMDS"
@@ -74,11 +77,13 @@
 	bool "Support suvd3"
 	imply CMD_CRAMFS
 	imply FS_CRAMFS
+	imply ENV_IS_IN_FLASH
 
 config TARGET_TUXX1
 	bool "Support tuxx1"
 	imply CMD_CRAMFS
 	imply FS_CRAMFS
+	imply ENV_IS_IN_FLASH
 
 config TARGET_TQM834X
 	bool "Support TQM834x"
@@ -90,6 +95,7 @@
 config TARGET_STRIDER
 	bool "Support strider"
 	select SYS_FSL_ERRATUM_ESDHC111
+	imply ENV_IS_IN_FLASH
 
 endchoice
 
diff --git a/arch/powerpc/cpu/mpc85xx/Kconfig b/arch/powerpc/cpu/mpc85xx/Kconfig
index cf55136..0c74f1d 100644
--- a/arch/powerpc/cpu/mpc85xx/Kconfig
+++ b/arch/powerpc/cpu/mpc85xx/Kconfig
@@ -19,6 +19,7 @@
 config TARGET_SBC8548
 	bool "Support sbc8548"
 	select ARCH_MPC8548
+	imply ENV_IS_IN_FLASH
 
 config TARGET_SOCRATES
 	bool "Support socrates"
@@ -104,6 +105,7 @@
 config TARGET_MPC8548CDS
 	bool "Support MPC8548CDS"
 	select ARCH_MPC8548
+	imply ENV_IS_IN_FLASH
 
 config TARGET_MPC8555CDS
 	bool "Support MPC8555CDS"
@@ -549,6 +551,7 @@
 	select SYS_FSL_SEC_BE
 	select SYS_FSL_SEC_COMPAT_2
 	select SYS_PPC_E500_USE_DEBUG_TLB
+	imply ENV_IS_IN_FLASH
 
 config ARCH_MPC8555
 	bool
@@ -596,6 +599,7 @@
 	select SYS_FSL_SEC_COMPAT_2
 	select SYS_PPC_E500_USE_DEBUG_TLB
 	select FSL_ELBC
+	imply ENV_IS_IN_FLASH
 
 config ARCH_P1010
 	bool
diff --git a/arch/powerpc/cpu/mpc86xx/Kconfig b/arch/powerpc/cpu/mpc86xx/Kconfig
index 2cc180d..fe56efd 100644
--- a/arch/powerpc/cpu/mpc86xx/Kconfig
+++ b/arch/powerpc/cpu/mpc86xx/Kconfig
@@ -40,6 +40,7 @@
 	select FSL_LAW
 	select SYS_FSL_HAS_DDR1
 	select SYS_FSL_HAS_DDR2
+	imply ENV_IS_IN_FLASH
 
 config FSL_LAW
 	bool