Defer pyftdi import: only import when --cpld option is used

Previously, the pyftdi module was imported unconditionally, causing
errors even when CPLD functionality was not required.
Now the import is performed only if the `--cpld` option is used,
avoiding unnecessary failures and improving script flexibility.

Signed-off-by: Mykhailo Androsiuk <mykhailo_androsiuk@epam.com>

Author: Mykhailo Androsiuk

rcar_flash/rcar_flash.py

@@ -197,6 +197,14 @@ def do_flash(conf, args):
         if "cpld_profile" not in board:
             raise Exception(
                 "'cpld_profile' is not set for board, can't control CPLD")
+        if args.cpld:
+            try:
+                import pyftdi  # noqa: F401
+            except ModuleNotFoundError:
+                raise Exception(
+                    "pyftdi module is required for CPLD usage but not found.\n"
+                    "Please install it via 'pip3 install --user pyftdi' or appropriate package manager."
+                    )
 
         # Force enable uploading flash_writer, otherwise it have no sense
         # to use CPLD
@@ -381,19 +389,6 @@ def get_srec_load_addr(fname):
     raise Exception(f"Could not read srec load address (S3) from {fname}")
 
 
-# CPLD Code begins there
-try:
-    import pyftdi
-    cpld_available = True
-except ModuleNotFoundError:
-    log.error("pyftdi module not found. CPLD Functinality is disabled.")
-    log.error("   Please install the module.")
-    log.error("   You can try \"pip3 install --user pyftdi\"")
-    log.error(
-        "   Or use your favourite packet manager (\"apt install python3-ftdi\" perhaps?)"
-    )
-
-
 def cpld_determine_serial(cpld_profile, args) -> str:
     import pyftdi.usbtools
     # Try to determine USB device serial number where CPLD resides