psci: rename psci_features function

s/psci_features/request_psci_features/g for the case when both
ARCH_SUPPORT_PSCI=y and ARM_PSCI_FW=y, that leads to these
compilation issues:

drivers/firmware/psci.c:69:12: error: conflicting types for 'psci_features'
   69 | static int psci_features(u32 psci_func_id)
      |            ^~~~~~~~~~~~~
In file included from drivers/firmware/psci.c:23:
./arch/arm/include/asm/system.h:548:5: note: previous declaration of 'psci_features' was here
  548 | s32 psci_features(u32 function_id, u32 psci_fid);
      |     ^~~~~~~~~~~~~

Tested-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
Reported-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
Fixes: b7135b03 ("psci: add features/reset2 support")
Signed-off-by: Igor Opaniuk <igor.opaniuk@foundries.io>