armv7: ls1021a: Convert CONFIG_LS1_DEEP_SLEEP to Kconfig option

Move this option to Kconfig and clean up existing uses.

Signed-off-by: York Sun <york.sun@nxp.com>
CC: Hongbo Zhang <hongbo.zhang@nxp.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 1bc45ed..5073930 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -822,6 +822,7 @@
 	select SUPPORT_SPL
 	select ARCH_LS1021A
 	select ARCH_SUPPORT_PSCI
+	select LS1_DEEP_SLEEP
 
 config TARGET_LS1021ATWR
 	bool "Support ls1021atwr"
@@ -829,6 +830,7 @@
 	select SUPPORT_SPL
 	select ARCH_LS1021A
 	select ARCH_SUPPORT_PSCI
+	select LS1_DEEP_SLEEP
 
 config TARGET_LS1043AQDS
 	bool "Support ls1043aqds"