qemu: update u-boot config fragment for v2019.01 to v2020.04

Update U-Boot config fragment to explicitly state no flash or MTD device
is used by U-Boot and the U-Boot environment is not stored outside
U-Boot image. This change is required since U-Boot v2019.01. It
successfully boots Qemu/armv7-A with older and newer U-Boot releases up
to v2020.04, and at least also up to latest U-boot RC tag v2020.07-rc3.

Signed-off-by: Etienne Carriere <etienne.carriere@linaro.org>
Acked-by: Joakim Bech <joakim.bech@linaro.org>
Acked-by: Jens Wiklander <jens.wiklander@linaro.org>

kconfigs/u-boot_qemu_virt_v7.conf

 CONFIG_SYS_TEXT_BASE=0x60000000
 CONFIG_BOOTCOMMAND="fdt addr ${fdt_addr} && fdt resize 1000 && smhload zImage ${kernel_addr_r} && smhload rootfs.cpio.gz ${ramdisk_addr_r} ramdisk_addr_end &&  setenv bootargs console=ttyAMA0,115200 earlyprintk=serial,ttyAMA0,115200 && fdt chosen ${ramdisk_addr_r} ${ramdisk_addr_end} && bootz ${kernel_addr_r} - ${fdt_addr}"
 CONFIG_SEMIHOSTING=y
+CONFIG_ENV_IS_NOWHERE=y
+# CONFIG_ENV_IS_IN_FLASH is not set
+# CONFIG_MTD is not set
+# CONFIG_MTD_NOR_FLASH is not set