Match AOSP get/set_bootloader_message() layouts

No change in behavior, just matching AOSP's code layout. LOGE has been
changed to LOGI for "Cannot load volume /misc!" since many devices do
not define a /misc partition in fstab.

Change-Id: I53c440f820fd4614b0af79e9283baa8c48453373
Remove obsolete check on device_flash_type() before trying to read args from BCB

get_bootloader_args() has handled the case where the misc partition
doesn't exist or is an unknown type since 7501798f... ("Fix nullpointer
when recovery.fstab does not define a "misc" partition") all the way
back in 2010, and we use set_bootloader_args() below unconditionally
anyway.  Remove this obsolete check.

Change-Id: Ie25083a6d24cf918f72cc1cc13b181292c61d160