Fix EFI UFS caching

Fix EFI UFS caching

EFI was mixing caching in two separate places causing issues when multiple
partitions where tested.

Eliminate this by removing fsstat and re-factoring fsread into fsread_size,
adding basic parameter validation.

Also:
* Enhance some error print outs.
* Fix compilation under UFS1_ONLY and UFS2_ONLY
* Use sizeof on vars instead of structs.
* Add basic parameter validation to fsread_size.

MFC after:	1 week
X-MFC-With:	r293268
Sponsored by:	Multiplay
Differential Revision:	https://reviews.freebsd.org/D4989