pmb.flasher: Fix passing command line flags
Commit 37ec73c0 dropped the use of args to access command line arguments, but did not add another way to pass command line arguments; thus, optional flags to flash_kernel, flash_rootfs, flash_lk2nd, sideload and list_devices were ignored.
Fix this by making sure the relevant arguments are passed for all frontend methods.
Fixes #2522 (closed), pmaports#3500 (closed).
Edited by knuxify