TF-A Tests: Enable PAuth on warm boot path

This patch provides the following features and makes
modifications listed below:
- `plat_init_apiakey()` function is replaced with `init_apkey()`
  which returns 128-bit value and uses Generic timer physical counter
  value to increase the randomness of the generated key.
  The new function can be used for generation of all ARMv8.3-PAuth keys.
- Source file `pauth.c` moved from `plat/common/aarch64`
  to `lib/extensions/pauth/aarch64` folder which contains PAuth specific
  code.
- Individual APIAKey key generation for each CPU on every warm boot.
- Per-CPU storage of APIAKey added in `tftf_suspend_context` structure.
- APIAKey key is saved/restored in arch context on entry/exit from
  suspended state.
- Added `pauth_init_enable()` function which generates, programs
  and enables APIAKey in EL1/EL2.
- Changes in documentation related to ARMv8.3-PAuth support.

Signed-off-by: Alexei Fedorov <Alexei.Fedorov@arm.com>
Change-Id: I964b8f964bb541cbb0b2f772cb0b07aed055fe36
diff --git a/tftf/framework/main.c b/tftf/framework/main.c
index e84e450..a2e84b7 100644
--- a/tftf/framework/main.c
+++ b/tftf/framework/main.c
@@ -12,6 +12,7 @@
 #include <irq.h>
 #include <mmio.h>
 #include <nvm.h>
+#include <pauth.h>
 #include <plat_topology.h>
 #include <platform.h>
 #include <platform_def.h>
@@ -528,19 +529,12 @@
 #if ENABLE_PAUTH
 	assert(is_armv8_3_pauth_apa_api_present());
 
-	uint64_t *apiakey = plat_init_apiakey();
-
-	write_apiakeylo_el1(apiakey[0]);
-	write_apiakeyhi_el1(apiakey[1]);
-
-	if (IS_IN_EL2()) {
-		write_sctlr_el2(read_sctlr_el2() | SCTLR_EnIA_BIT);
-	} else {
-		assert(IS_IN_EL1());
-		write_sctlr_el1(read_sctlr_el1() | SCTLR_EnIA_BIT);
-	}
-
-	isb();
+	/*
+	 * Program APIAKey_EL1 key and enable ARMv8.3-PAuth here as this
+	 * function doesn't return, and RETAA instuction won't be executed,
+	 * what would cause translation fault otherwise.
+	 */
+	pauth_init_enable();
 #endif /* ENABLE_PAUTH */
 
 	tftf_platform_setup();