loader: Fix 32-bit compatibility

main.c - Fix rsdp cast.
framebuffer.c -

• Use temp variable instead of directly passing pointer when EFI_PHYSICAL_ADDRESS is expected.

	  Also fix FreePages cast.

• Mask framebuffer address given to us by UEFI.

Reviewed by: imp
Pull Request: https://github.com/freebsd/freebsd-src/pull/1098