refactor(st): move GIC code to common directory

The GIC v2 initialization code could be shared to other ST platforms.
The stm32mp1_gic.c file is then moved to common directory, and renamed
stm32mp_gic.c.
The functions are also prefixed with stm32mp_gic.

Change-Id: I60820823b470217d3a95cc569f941c2cb923dfa9
Signed-off-by: Yann Gautier <yann.gautier@st.com>
diff --git a/plat/st/stm32mp1/include/stm32mp1_private.h b/plat/st/stm32mp1/include/stm32mp1_private.h
index 21ef60d..4a52255 100644
--- a/plat/st/stm32mp1/include/stm32mp1_private.h
+++ b/plat/st/stm32mp1/include/stm32mp1_private.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2015-2022, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2015-2023, ARM Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -14,9 +14,6 @@
 void stm32mp1_arch_security_setup(void);
 void stm32mp1_security_setup(void);
 
-void stm32mp1_gic_pcpu_init(void);
-void stm32mp1_gic_init(void);
-
 void stm32mp1_syscfg_init(void);
 void stm32mp1_syscfg_enable_io_compensation_start(void);
 void stm32mp1_syscfg_enable_io_compensation_finish(void);