microblaze: migrate CONFIG_SYS_USR_EXCEP to Kconfig

Migrate CONFIG_SYS_USR_EXCEP to Kconfig. Also, rename it to
XILINX_MICROBLAZE0_USR_EXCEP in order to match the naming convention of
microblaze-generic Kconfig options.

Signed-off-by: Ovidiu Panait <ovidiu.panait@windriver.com>
Link: https://lore.kernel.org/r/20211130163358.2531677-7-ovidiu.panait@windriver.com
Signed-off-by: Michal Simek <michal.simek@xilinx.com>
diff --git a/arch/microblaze/cpu/start.S b/arch/microblaze/cpu/start.S
index 74ed998..68f97f4 100644
--- a/arch/microblaze/cpu/start.S
+++ b/arch/microblaze/cpu/start.S
@@ -144,7 +144,7 @@
 	rsubi	r8, r10, 0x6
 	sh	r6, r0, r8
 
-#ifdef CONFIG_SYS_USR_EXCEP
+#if CONFIG_IS_ENABLED(XILINX_MICROBLAZE0_USR_EXCEP)
 	/* user_vector_exception */
 	swi	r2, r0, 0x8	/* user vector exception - imm opcode */
 	swi	r3, r0, 0xC	/* user vector exception - brai opcode */