ARM: renesas: Set CONFIG_SYS_TEXT_BASE=0x0 on R-Car Gen3

Since R-Car Gen3 already enables position independent build, also set
CONFIG_SYS_TEXT_BASE=0x0 to finalize the switch. This is possible since
534f0fbd65 ("arm64: Fix relocation of env_addr if POSITION_INDEPENDENT=y")
fixed current env_get_char() crash with CONFIG_SYS_TEXT_BASE=0x0 .

This change permits us to start U-Boot from any location in DRAM instead
of specific TEXT_BASE.

Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>
diff --git a/configs/rcar3_salvator-x_defconfig b/configs/rcar3_salvator-x_defconfig
index ab996dd8..7bebdf0 100644
--- a/configs/rcar3_salvator-x_defconfig
+++ b/configs/rcar3_salvator-x_defconfig
@@ -1,7 +1,7 @@
 CONFIG_ARM=y
 CONFIG_ARCH_CPU_INIT=y
 CONFIG_ARCH_RMOBILE=y
-CONFIG_SYS_TEXT_BASE=0x50000000
+CONFIG_SYS_TEXT_BASE=0x0
 CONFIG_ENV_SIZE=0x20000
 CONFIG_ENV_OFFSET=0xFFFE0000
 CONFIG_DM_GPIO=y