corstone1000: Convert to text file environment

Convert this platform to using the text file environment rather than
defining CONFIG_EXTRA_ENV_SETTINGS.

Signed-off-by: Tom Rini <trini@konsulko.com>

board/armltd/corstone1000/corstone1000.env

@@ -0,0 +1,13 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+
+usb_pgood_delay=250
+boot_bank_flag=0x08002000
+kernel_addr_bank_0=0x083EE000
+kernel_addr_bank_1=0x0936E000
+retrieve_kernel_load_addr=
+	if itest.l *${boot_bank_flag} == 0; then
+		setenv kernel_addr $kernel_addr_bank_0;
+	else
+		setenv kernel_addr $kernel_addr_bank_1;
+	fi;
+kernel_addr_r=0x88200000