libefi only use waitforkeys if available

[manu]

Summary

Only use WaitForKeys event if it exists, this is not the case in u-boot efi implementation.

Test Plan

Tested on beaglebone black with u-boot efi implementation.

[andrew]

This looks correct, but add some UEFI people to check. On U-Boot WaitForKey is NULL.

[imp]

sys/boot/efi/libefi/efi_console.c

442 ↗

(On Diff #17445)

This check should be against zero since this isn't a bool or even a pointer.

[manu]

sys/boot/efi/libefi/efi_console.c

442 ↗

(On Diff #17445)

From sys/boot/efi/include/efidef.h :
typedef VOID *EFI_EVENT;

So I should check against NULL.

[manu]

Check against NULL

[emaste]

LGTM. Perhaps worth a comment in the source referencing u-boot UEFI as an example of an impl. lacking WaitForEvent?