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