spl: introduce SPL_XIP to config

U-Boot and SPL don't necessary share the same location, so we might end
with U-Boot SPL in read-only memory (XIP) and U-Boot in read-write memory.

In case of non XIP boot mode, we rely on such variables as "hart_lottery"
and "available_harts_lock" which we use as atomics.

The problem is that CONFIG_XIP also propagate to main U-Boot, not only SPL,
so we need CONFIG_SPL_XIP to distinguish SPL XIP from other XIP modes.

This adds an option special for SPL to behave it in XIP manner and we don't
use hart_lottery and available_harts_lock, during start proccess.

Signed-off-by: Nikita Shubin <n.shubin@yadro.com>
Reviewed-by: Rick Chen <rick@andestech.com>
diff --git a/configs/ae350_rv64_spl_xip_defconfig b/configs/ae350_rv64_spl_xip_defconfig
index a197c97..baee9bf 100644
--- a/configs/ae350_rv64_spl_xip_defconfig
+++ b/configs/ae350_rv64_spl_xip_defconfig
@@ -12,7 +12,7 @@
 CONFIG_TARGET_AX25_AE350=y
 CONFIG_ARCH_RV64I=y
 CONFIG_RISCV_SMODE=y
-CONFIG_XIP=y
+CONFIG_SPL_XIP=y
 CONFIG_DISTRO_DEFAULTS=y
 CONFIG_HAS_CUSTOM_SYS_INIT_SP_ADDR=y
 CONFIG_CUSTOM_SYS_INIT_SP_ADDR=0xfffe70